OK, .NET noob here (as in I know next to nothing, I’m trying to pick up some of the scraps left by my developer).
Ok, I am getting this error on a number of my .aspx pages:
Error while checking url ‘/’: Key cannot be null. Parameter name: key
Interestingly, I get this on my homepage on which the only .NET code is in the form of two includes, e.g:
<% Response.WriteFile(“/includes/footer.aspx”) %>
These includes in themselves only contain HTML, so I assume the issue can only be related to these or a configuration issue?
Could someone please point me in the right direction? 
Thanks! 
How about the includes? There is nothing to look at in the code posted.
Header:
<div id="wrapper">
<div id="container">
<div id="header">
<div id="logo"><a href="/">TenthTime.com</a></div>
<div id="search">
<form action="#" method="post">
<fieldset>
<input type="text" id="textfield" />
<input type="image" class="btn" src="/images/go.png"/>
</fieldset>
</form>
</div>
</div>
<div id="nav">
<ul>
<li id="nav-entertainment" class="dropdown"><a href="/entertainment/default.aspx">Entertainment</a>
<ul id="sub-entertainment" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="#">Accessories</a></li>
<li><a href="#">Baby Carriers</a></li>
<li><a href="#">Baby Monitors</a></li>
<li><a href="#">Baby Skincare</a></li>
<li><a href="#">Baby Walkers</a></li>
<li><a href="#">Bathing</a></li>
</ul></li>
<li><ul class="right">
<li><a href="#">Carriers</a></li>
<li><a href="#">Changing Equipment</a></li>
<li><a href="#">Cots</a></li>
<li><a href="#">Cribs & Cradles</a></li>
<li><a href="#">Gifts</a></li>
<li><a href="/entertainment/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-electronics" class="dropdown"><a href="/electronics/default.aspx">Electronics</a>
<ul id="sub-electronics" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/electronics/audio/default.aspx">Audio</a></li>
<li><a href="/electronics/blu-ray-and-dvd-players/default.aspx">Blu-ray & DVD</a></li>
<li><a href="/cables-and-parts/default.aspx">Cables & Parts</a></li>
<li><a href="/cameras-and-camcorders/default.aspx">Cameras & Camcorders</a></li>
<li><a href="/electronics/computing/computers/desktops/default.aspx">Desktop Computers</a></li>
<li><a href="/electronics/computing/computers/laptops/default.aspx">Laptops</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/electronics/gps-and-sat-nav/default.aspx">GPS & Sat Nav</a></li>
<li><a href="/electronics/projectors/default.aspx">Projectors</a></li>
<li><a href="/electronics/telephones-and-fax-machines/default.aspx">Telephones & Faxes</a></li>
<li><a href="/electronics/televisions/default.aspx">Televisions</a></li>
<li><a href="/electronics/wireless-and-networking/default.aspx">Wireless & Networking</a></li>
<li><a href="/electronics/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-home-and-garden" class="dropdown"><a href="/home-and-garden/default.aspx">Home and Gardem</a>
<ul id="sub-home" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/home-and-garden/appliances/default.aspx">Appliances</a></li>
<li><a href="/home-and-garden/bathroom/default.aspx">Bathroom</a></li>
<li><a href="/home-and-garden/diy-equipment/default.aspx">DIY Equipment</a></li>
<li><a href="/home-and-garden/furniture/default.aspx">Furniture</a></li>
<li><a href="/home-and-garden/garden/default.aspx">Garden</a></li>
<li><a href="/home-and-garden/home-dressing/default.aspx">Home Dressing</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/home-and-garden/kitchen/default.aspx">Kitchen</a></li>
<li><a href="/home-and-garden/lighting/default.aspx">Lighting</a></li>
<li><a href="/home-and-garden/security/default.aspx">Security</a></li>
<li><a href="/home-and-garden/storage/default.aspx">Storage</a></li>
<li><a href="/home-and-garden/travelling/default.aspx">Travelling</a></li>
<li><a href="/home-and-garden/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-office" class="dropdown"><a href="/office/default.aspx">Office</a>
<ul id="sub-office" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/office/binding/default.aspx">Binding</a></li>
<li><a href="/office/desk-accessories/default.aspx">Desk Accessories</a></li>
<li><a href="/office/dictation-machines/default.aspx">Dictation Machines</a></li>
<li><a href="/office/laminating/default.aspx">Laminating</a></li>
<li><a href="/office/office-furniture/default.aspx">Office Furniture</a></li>
<li><a href="/office/photocopiers/default.aspx">Photocopiers</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/office/presentations/default.aspx">Presentations</a></li>
<li><a href="/office/printer-supplies/default.aspx">Printer Supplies</a></li>
<li><a href="/office/shredders/default.aspx">Shredders</a></li>
<li><a href="/office/stationary/default.aspx">Stationary</a></li>
<li><a href="/office/whiteboards-and-noticeboards/default.aspx">Whiteboards</a></li>
<li><a href="/office/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-health-and-beauty" class="dropdown"><a href="/health-and-beauty/default.aspx">Health and Beauty</a>
<ul id="sub-health" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/health-and-beauty/bodycare-appliances/default.aspx">Bodycare Appliances</a></li>
<li><a href="/health-and-beauty/cosmetics-and-skincare/default.aspx">Cosmetics and Skincare</a></li>
<li><a href="/health-and-beauty/fragrance/default.aspx">Fragrance</a></li>
<li><a href="/health-and-beauty/haircare/default.aspx">Haircare</a></li>
<li><a href="/health-and-beauty/medical-supplies/default.aspx">Medical Supplies</a></li>
<li><a href="/health-and-beauty/oral-health/default.aspx">Oral Health</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/health-and-beauty/shaving/default.aspx">Shaving</a></li>
<li><a href="/health-and-beauty/vitamins-and-supplements/default.aspx">Vitamins & Supplements</a></li>
<li><a href="/health-and-beauty/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-sports" class="dropdown"><a href="/sport-and-fitness/default.aspx">Sports</a>
<ul id="sub-sports" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/sport-and-fitness/cycling/default.aspx">Cycling</a></li>
<li><a href="/sport-and-fitness/extreme-sports/default.aspx">Extreme Sports</a></li>
<li><a href="/sport-and-fitness/fishing/default.aspx">Fishing</a></li>
<li><a href="/sport-and-fitness/fitness-equipment/default.aspx">Fitness Equipment</a></li>
<li><a href="/sport-and-fitness/football/default.aspx">Football</a></li>
<li><a href="#">Bathing</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/sport-and-fitness/golf/default.aspx">Golf</a></li>
<li><a href="/sport-and-fitness/golf/default.aspx">Skateboarding</a></li>
<li><a href="/sport-and-fitness/snooker-and-pool/default.aspx">Snooker & Pool</a></li>
<li><a href="/sport-and-fitness/tennis/default.aspx">Tennis</a></li>
<li><a href="/sport-and-fitness/winter-sports/default.aspx">Winter Sports</a></li>
<li><a href="/sport-and-fitness/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-jewellery" class="dropdown"><a href="/jewellery/default.aspx">Jewellery</a>
<ul id="sub-jewellery" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/jewellery/womens-jewellery/accessories/default.aspx">Women's Accessories</a></li>
<li><a href="/jewellery/womens-jewellery/bracelets/default.aspx">Women's Bracelets</a></li>
<li><a href="/jewellery/womens-jewellery/earrings/default.aspx">Women's Earrings</a></li>
<li><a href="/jewellery/womens-jewellery/necklaces/default.aspx">Women's Necklaces</a></li>
<li><a href="/jewellery/womens-jewellery/rings/default.aspx">Women's Rings</a></li>
<li><a href="/jewellery/womens-watches/default.aspx">Women's Watches</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/jewellery/mens-jewellery/bracelets/default.aspx">Men's Bracelets</a></li>
<li><a href="/jewellery/mens-jewellery/cufflinks/default.aspx">Men's Cufflinks</a></li>
<li><a href="/jewellery/mens-jewellery/necklaces/default.aspx">Men's Necklaces</a></li>
<li><a href="/jewellery/mens-jewellery/rings/default.aspx">Men's Rings</a></li>
<li><a href="/jewellery/mens-watches/default.aspx">Men's Watches</a></li>
<li><a href="/jewellery/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-family" class="dropdown"><a href="/family/default.aspx">Family</a>
<ul id="sub-family" class="submenu">
<li><div class="arrow"></div></li>
<li><ul>
<li><ul class="left">
<li><a href="/family/accessories/default.aspx">Accessories</a></li>
<li><a href="/family/baby-monitors/default.aspx">Baby Monitors</a></li>
<li><a href="/family/bathing/default.aspx">Bathing</a></li>
<li><a href="/family/car-seats/default.aspx">Car Seats</a></li>
<li><a href="/family/carriers/default.aspx">Carriers</a></li>
<li><a href="/family/childrens-toys/default.aspx">Children's Toys</a></li>
</ul></li>
<li><ul class="right">
<li><a href="/family/cots/default.aspx">Cots</a></li>
<li><a href="/family/highchairs/default.aspx">Highchairs</a></li>
<li><a href="/family/nursery/default.aspx">Nursery</a></li>
<li><a href="/family/prams-pushchairs-amp-buggies/default.aspx">Prams & Puschairs</a></li>
<li><a href="/family/travelling/default.aspx">Travelling</a></li>
<li><a href="/family/default.aspx"><strong>More Categories...</strong></a></li>
</ul>
</li>
</ul></li>
</ul>
</li>
<li id="nav-by-store" class="dropdown"><a href="#">View by Store</a></li>
</ul>
</div>
<div id="alpha">
<ul>
<li><a href="#">A</a></li>
<li><a href="#">B</a></li>
<li><a href="#">C</a></li>
<li><a href="#">D</a></li>
<li><a href="#">E</a></li>
<li><a href="#">F</a></li>
<li><a href="#">G</a></li>
<li><a href="#">H</a></li>
<li><a href="#">I</a></li>
<li><a href="#">J</a></li>
<li><a href="#">K</a></li>
<li><a href="#">L</a></li>
<li><a href="#">M</a></li>
<li><a href="#">N</a></li>
<li><a href="#">O</a></li>
<li><a href="#">P</a></li>
<li><a href="#">Q</a></li>
<li><a href="#">R</a></li>
<li><a href="#">S</a></li>
<li><a href="#">T</a></li>
<li><a href="#">U</a></li>
<li><a href="#">V</a></li>
<li><a href="#">W</a></li>
<li><a href="#">X</a></li>
<li><a href="#">Y</a></li>
<li><a href="#">Z</a></li>
<li><a href="#">#</a></li>
</ul>
</div>
Footer:
<div id="footer">
<div class="ftr"><div class="ftrlt"> Copyright © TenthTime.com 2010. All Rights Reserved.</div>
<div class="ftrrt"><a href="#">About Us</a> | <a href="#">Featured Brands</a> | <a href="#">Help</a> | <a href="#">FAQ’s</a> | <a href="#">Terms of Use</a> |<br />
<span class="green">Valid <a href="#">XHTML</a> &<a href="#"> CSS</a></span></div>
</div>
</div>
</div>
These are both just plain HTML.
Thanks for your reply, here’s the source code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Tenth Time</title>
<link rel="stylesheet" type="text/css" href="css/default.css"/>
<link rel="stylesheet" type="text/css" href="css/sifr.css"/>
<link rel="stylesheet" type="text/css" href="css/nav.css"/>
<script src="js/sf-focus.js" type="text/javascript"></script>
<script src="js/sifr/sifr.js" type="text/javascript"></script>
<script src="js/sifr/sifr-config.js" type="text/javascript"></script>
<script src="js/subnav.js" type="text/javascript"></script>
</head>
<body >
<% Response.WriteFile("/includes/header.aspx") %>
<div id="content">
<div id="ltpanel">
<div class="tab">
<h3 id="about">What we're all about</h3>
<div class="tabcnt">
<p>Put simply, we're here to make it easier for you to shop online. We take the best products from the biggest brands and put them in one place.</p>
<div class="divider"></div>
<blockquote id="homecomment">
<p>What's the point in visiting site after site, when you can find all you're looking for on one?</p></blockquote>
<div class="divider"></div>
<p>Learn more about TenthTime.com and what we stand for.</p>
<div id="learn-more-btn"><a href="#">Learn more about us</a></div>
</div>
<div class="btm"></div>
</div>
<div class="tab">
<h3 class="onlineshop">The Online Shopping Centre</h3>
<div class="tabcnt">
<div class="img"><img src="images/ltpanel/shopping-img.png" alt="The Online Shopping Centre" width="185" height="104" />
<p>Think of us, not as a store, but more like an online shopping centre - or a virtual
high street. Why not take a stroll? </p>
<h4 id="best-deals">All the best deals</h4>
<p>We bring you the best prices from all of your favourtive online stores.We're sure you'll find the best deal right here.</p>
<div class="dbl-divider"></div>
<p class="last-p"><a href="#">See a full list of our featured brands...</a></p></div>
</div>
<div class="btm"></div>
</div>
<div class="tab">
<h3 class="help">Help and Assistance</h3>
<div class="tabcnt">
<div>
<p>Have a question or would like some help using our site? No problem, visit <a href="#">our help section</a> for a details of how to get in touch with us.</p>
<h4 id="faq">Frequently Asked Questions</h4>
<p>To get an answer straight away, you may be able to find what you're looking for in our FAQ section.</p>
<ul>
<li><a href="#">Frequently Asked Questions</a></li>
</ul>
<div id="help-icon"></div>
</div>
</div>
<div class="btm"></div>
<div class="snippet">
<h4 id="tip-1">Top Tip #1</h4>
<p>If you know the full name of the item you're looking for, enter it into the search
box in the top right to find it more quickly.</p>
<div class="dbl-divider"></div>
</div>
</div>
</div>
<ul id="breadcrumb" >
<li id="bchome"><a href="#"></a></li>
<li>Welcome to TenthTime.com</li>
</ul>
<div id="main">
<div id="contentbox">
<div class="box">
<h1>Find Everything You're Looking for in a <em>Tenth</em> of the <em>Time</em></h1>
<p>Welcome to TenthTime.com, the online shopping centre where you can find just about anything you're looking to buy. Books, homeware, electrical items - you name it, it's here. Featuring all of the best products from all of your favourite brands, we take the stress out of online shopping whether you're looking for youself or someone else.</p></div>
<div class="box">
<div class="bx">
<div class="head">
<h3 id="entertainment"><a href="#">Entertainment</a></h3></div>
<p>Featuring books, DVD's and games our entertainment section is filled with fun stuff from a whole host of great brands.</p>
<ul>
<li class="pink"><a href="#">Go to Entertainment</a></li>
</ul>
</div>
<div class="bx">
<div class="head">
<h3 id="electronics"><a href="#">Electronics</a></h3></div>
<p>TV's, MP3 players, computers and more. There are some great deals to be had on all of the latest electrical equipment.</p>
<ul>
<li class="pink"><a href="#">Go to Electronics</a></li>
</ul>
</div>
<div class="cls"></div>
</div>
<div class="box">
<div class="bx">
<div class="head">
<h3 id="home-garden"><a href="#">Home & Garden</a></h3></div>
<p>Transform your home, inside and out. Whether it's furniture, kitchen appliances or something for your garden, you'll find it in here.</p>
<ul>
<li class="green"><a href="#"> Go to Home & Garden</a></li>
</ul>
</div>
<div class="bx">
<div class="head">
<h3 id="office"><a href="#">Office</a></h3></div>
<p>Make the most of your working environment at work or at home by refreshing it with new office furniture and equipment.</p>
<ul>
<li class="green"><a href="#">Go to Office </a></li>
</ul>
</div>
<div class="cls"></div>
</div>
<div class="box">
<div class="bx">
<div class="head">
<h3 id="health-beauty"><a href="#">Health & Beauty</a></h3></div>
<p>We know it's important for you to look and feel your best at all times. That's why we've got everything you need to do just that.</p>
<ul>
<li class="yellow"><a href="#">Go to Health & Beauty</a></li>
</ul>
</div>
<div class="bx">
<div class="head">
<h3 id="sports-fitness"><a href="#">Sports & Fitness</a></h3></div>
<p>Whether you're a fitness freak, sports enthusiast or just looking to lose a few pounds, there's plenty here to help you on your way.</p>
<ul>
<li class="yellow"><a href="#">Go to Sports & Fitness</a></li>
</ul>
</div>
<div class="cls"></div>
</div>
<div class="box">
<div class="bx">
<div class="head">
<h3 id="jewellery-watches"><a href="#">Jewellery & Watches</a></h3></div>
<p>Great savings on jewellery and watches from a wealth of the UK's most respected brands - no matter what your budget.</p>
<ul>
<li class="blue"><a href="#">Go to Jewellery</a></li>
</ul>
</div>
<div class="bx">
<div class="head">
<h3 id="family"><a href="#">Family</a></h3></div>
<p>Fantastic deals on baby and nursey products, toys and more from the most trusted brands in the business.</p>
<ul>
<li class="blue"><a href="#">Go to Family </a></li>
</ul>
</div>
<div class="cls"></div>
</div>
<div class="taba">
<h3 id="great-brands">So Many Great Brands</h3>
<div class="tabcnt-b">
<div id="hp-banner">
</div>
</div>
<div class="btm"></div>
</div>
</div><div id="rtpanel">
<div class="tab">
<h3 id="getting-started">Getting-started</h3>
<div class="tabcnt">
<p>Using our site simply couldn't be any easier. To get started, all you need to do is follow the steps below. </p>
<ul class="ul">
<li class="divider"></li>
<li id="a">Use the site navigation to find what you want</li>
<li class="divider"></li>
<li id="b"> Click 'buy now' - you'll be aken to the store selling your item.</li>
<li class="divider"></li>
<li id="c">Follow the store's instruction to complete the transaction</li>
</ul>
</div>
<div class="btm"></div>
</div>
<div></div>
<div id="testimonial">
<p>It took me less than half-an-hour to do nearly all of my Christmas shopping. Great stuff!</p>
</div>
<div id="testimonial-btm"></div>
<div class="tab">
<h3 id="spread">Spread The word</h3>
<div class="tabcnt" id="spread-word">
<p>If you like what you see, why not spread the word via your favourite social networking web site.</p>
<ul>
<li id="twitter"><a href="#">Twitter</a></li>
<li id="stumble"><a href="#">Stumble Upon</a></li>
<li id="digg"><a href="#">Digg</a></li>
<li id="facebook"><a href="#">Facebook</a></li>
<li id="delicious"><a href="#">Delicious</a></li>
</ul>
<h4 id="old-skool">Keepin' it Old Skool</h4>
<p class="last-p">Don't forget word of mouth - if you found our site useful then we'd love you to tell your friends about us!</p>
</div>
<div class="btm"></div>
</div>
<div class="snippet">
<h4 id="tip-2">Top Tip #2</h4>
<p>If you're looking for a true bargain, filtering your search results by 'lowest price' will help you track one down. </p></div>
<div class="snippet">
<h4 id="tip-3">Top Tip #3</h4>
<p>Sometimes our partners will have additional special offers on their site. Click 'more information' to find out.</p>
<div class="dbl-divider"></div>
</div>
</div>
</div>
</div>
</div>
<div class="cls"></div>
<% Response.WriteFile("/includes/footer.aspx") %>
</body>
</html>
I believe MasterPages were introduced in ASP.NET 2 so that would imply that it was written using version 1 (or 1.1) a long time ago.
It’s hard to tell what’s going on without some view of the source.