Cannot send session cache limiter - headers already sent

HI all, I have a bit of a head ache with a small bit of php that is driving me nuts.

I’m doing a bit of work for someone and the contact form is out putting an error. This is the (http://www.pembrokeshirewebsolutions.co.uk/test2/index.php)

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home1/pembrok1/public_html/pws.co.uk/test2/index.php:7) in /home1/pembrok1/public_html/pws.co.uk/test2/html-contact-form.php on line 4

However, html-contact-form.php reads like this

<?php 
$your_email ='iknowthis@hotmail.com';// <<=== update to your email address

session_start();
$errors = '';
$name = '';
$visitor_email = '';
$user_message = '';

if(isset($_POST['submit']))
{
	
	$name = $_POST['name'];
	$visitor_email = $_POST['email'];
	$user_message = $_POST['message'];
	///------------Do Validations-------------
	if(empty($name)||empty($visitor_email))
	{
		$errors .= "\
 Name and Email are required fields. ";	
	}
	if(IsInjected($visitor_email))
	{
		$errors .= "\
 Bad email value!";
	}
	if(empty($_SESSION['6_letters_code'] ) ||
	  strcasecmp($_SESSION['6_letters_code'], $_POST['6_letters_code']) != 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!";
	}
	
	if(empty($errors))
	{
		//send the email
		$to = $your_email;
		$subject="New form submission";
		$from = $your_email;
		$ip = isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : '';
		
		$body = "A user  $name submitted the contact form:\
".
		"Name: $name\
".
		"Email: $visitor_email \
".
		"Message: \
 ".
		"$user_message\
".
		"IP: $ip\
";	
		
		$headers = "From: $from \\r\
";
		$headers .= "Reply-To: $visitor_email \\r\
";
		
		mail($to, $subject, $body,$headers);
		
		header('Location: thank-you.html');
	}
}

// Function to validate against any email injection attempts
function IsInjected($str)
{
  $injections = array('(\
+)',
              '(\\r+)',
              '(\	+)',
              '(%0A+)',
              '(%0D+)',
              '(%08+)',
              '(%09+)'
              );
  $inject = join('|', $injections);
  $inject = "/$inject/i";
  if(preg_match($inject,$str))
    {
    return true;
  }
  else
    {
    return false;
  }
}
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 
<html>
<head>
	<title>Contact Us</title>
<!-- define some style elements-->
<style>
label,a, body 
{
	font-family : Arial, Helvetica, sans-serif;
	font-size : 12px; 
}
.err
{
	font-family : Verdana, Helvetica, sans-serif;
	font-size : 12px;
	color: red;
}
</style>	
<!-- a helper script for vaidating the form-->
<script language="JavaScript" src="scripts/gen_validatorv31.js" type="text/javascript"></script>	
</head>

<body>
<?php
if(!empty($errors)){
echo "<p class='err'>".nl2br($errors)."</p>";
}
?>
<div id='contact_form_errorloc' class='err'></div>
<form method="POST" name="contact_form" 
action="<?php echo htmlentities($_SERVER['PHP_SELF']); ?>"> 
<p>
<label for='name'>Name: </label><br>
<input type="text" name="name" value='<?php echo htmlentities($name) ?>'>
</p>
<p>
<label for='email'>Email: </label><br>
<input type="text" name="email" value='<?php echo htmlentities($visitor_email) ?>'>
</p>
<p>
<label for='message'>Message:</label> <br>
<textarea name="message" rows=8 cols=30><?php echo htmlentities($user_message) ?></textarea>
</p>
<p>
<img src="captcha_code_file.php?rand=<?php echo rand(); ?>" id='captchaimg' ><br>
<label for='message'>Enter the code above here :</label><br>
<input id="6_letters_code" name="6_letters_code" type="text"><br>
<small>Can't read the image? click <a href='javascript: refreshCaptcha();'>here</a> to refresh</small>
</p>
<input type="submit" value="Submit" name='submit'>
</form>
<script language="JavaScript">
// Code for validating the form
// Visit http://www.javascript-coder.com/html-form/javascript-form-validation.phtml
// for details
var frmvalidator  = new Validator("contact_form");
//remove the following two lines if you like error message box popups
frmvalidator.EnableOnPageErrorDisplaySingleBox();
frmvalidator.EnableMsgsTogether();

frmvalidator.addValidation("name","req","Please provide your name"); 
frmvalidator.addValidation("email","req","Please provide your email"); 
frmvalidator.addValidation("email","email","Please enter a valid email address"); 
</script>
<script language='JavaScript' type='text/javascript'>
function refreshCaptcha()
{
	var img = document.images['captchaimg'];
	img.src = img.src.substring(0,img.src.lastIndexOf("?"))+"?rand="+Math.random()*1000;
}
</script>
<noscript>
Code from the <a href='http://www.html-form-guide.com/contact-form/html-contact-form-captcha.html'
>php contact form</a> article.
</noscript>
</body>
</html>

Anyone have some suggestions?

Thanks in advance

html-contact-form.php must be called directly, not being included into index.php
or index.php should not output anything.

Everything is told in the error message

Can you expand a little on this, about being called directly?

<form method=“POST” name=“contact_form”
action=“html-contact-form.php”>

Hi I understand now, though could you see any problems using

<?php ob_start(); ?>

at the very top of the index.php page?

lack of sense only

Thansk for your help guys

NOW RESOLVED