Hoping someone might be able to help me fix up my code...

My contact form has been validating the name, email and comments box successfully using javascript until I added a captcha code to my contact form today (copy and pasting the captcha code from another page of my site booknow.php). Now the form won't validate and it just posts the form regardless of what values are inputted into the form. Thanks.

<form method="post"  onSubmit="return validateForm()" action="sendContact.php" id="contact" name="contact">
					<label for="name">Name:</label>
					<input type="text" value="Name" id="name" name="txtName" <?php if(!empty($errors)){ echo "value='".($name)."'"; } ?> />
					<label for="email">Email address:</label>
					<input type="text" value="Email address" id="email" name="txtEmail" <?php if(!empty($errors)){ echo "value='".($email)."'"; } ?> />
					<label for="enquiry">Your enquiry:</label>
					<textarea id="enquiry" value="Your enquiry" name="enquiry" />Your enquiry</textarea>

		<img src="captcha_code_file.php?rand=<?php echo rand(); ?>" id='captchaimg' ><br><br>

		<small>Can't read the image? click <a href='javascript: refreshCaptcha();'>here</a> to refresh</small><br><br>
<label for="input">Captcha code:</label>
		<input type="text" size="32" id="input" name="txtInput" <?php if(!empty($errors)){ echo "value='".($input)."'"; } ?> /><br><br>		

					<input type="image" alt="Submit" name="submit" id="submit" src="images/submit.jpg" />

    	<script type="text/javascript">
	function validateForm()


		var errorMessage="";

		var name=document.forms["contact"]["txtName"].value;

		var email=document.forms["contact"]["txtEmail"].value;		

		var input=document.forms["contact"]["txtInput"].value;

		var atpos=email.indexOf("@");

		var dotpos=email.lastIndexOf(".");

		if (name==null || name=="")


			errorMessage = "Your Name is required.\n";


		if (email==null || email=="")


			errorMessage += "Email address is required.\n";


		else if (atpos<1 || dotpos<atpos+2 || dotpos+2>=email.length)


			errorMessage += "Please enter a valid email address.\n";


		if (input==null || input=="")


			errorMessage += "Captcha code is required.\n";


function refreshCaptcha()


		var img = document.images['captchaimg'];

		img.src = img.src.substring(0,img.src.lastIndexOf("?"))+"?rand="+Math.random()*1000;

    if(empty($_SESSION['6_letters_code'] ) || strcasecmp($_SESSION['6_letters_code'], $_POST['txtInput']) != 0)


	//Note: the captcha code is compared case insensitively.

	//if you want case sensitive match, update the check above to

	// strcmp()

		$errors .= "The captcha code does not match";

$message = "Hi,

You have a new contact request.

From : ".$_POST['txtEmail']."
Name : ".$_POST['txtName']."
Message : ".$_POST['enquiry']."

Ready 2 Rock";

$headers = 'From: webmaster@ready2rock.com.au' . "\r\n" .
    'Reply-To: webmaster@ready2rock.com.au' . "\r\n" .
    'X-Mailer: PHP/' . phpversion();

    mail('daniela@ready2rock.com.au','Ready 2 Rock Contact Form',$message,$headers);