Hi everyone....can some kind soul help me fix this PHP script i'm struggling with, its doin me ed in!

Its a PHP email contact form with captcha.
The problem is with the captcha part of the script...the form will run and show errors for invalid fields exept for the captcha.....the capcha image displays and refreshes but the form is not processing the captcha function.
The form can be filled in and the emails sent but the captcha part of the script is dead....I hope this is a clear enough description.
Here's the code.
<?php
define("MAIL_TARGET","my email.com");
define("errorName","Invalid name! It must be at least 2 characters long");
define("errorEmail","Invalid email address!");
define("errorMsg","Invalid message! It must be at least 10 characters long");
define("errorCode","Security code is incorrect! please try again");
function createForm($name="",$email="",$message="",$error1= "",$error2="",$error3="",$error4=""){
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<table>
<tr><td>Name: </td><td class="error"><?php echo $error1; ?></td></tr>
<tr><td colspan="2"><input class="text" type="text" name="name" value="<?php echo $name; ?>"></td></tr>
<tr><td>Email:</td><td class="error"><?php echo $error2; ?></td></tr>
<tr><td colspan="2"><input class="text" type="text" name="email" value="<?php echo $email; ?>"></td></tr>
<tr><td>Message:</td><td class="error"><?php echo $error3; ?></td></tr>
<tr><td colspan="2"><textarea class="message" cols="42" rows="8" name="message"><?php echo $message; ?></textarea></td></tr>
<td ><p><img src='captcha.php?<?PHP echo time(); ?>' border='1'><br/>
<tr><td colspan="2"><input class="text" type="text" name="usercode" value="<?php echo $usercode; ?>"></td></tr>
<tr><td>Security Code:</td><td class="error"><?php echo $error4; ?></td></tr>
<tr><td colspan="2"><br/><input class="text" type="submit" name="submitBtn" value="Send email"></td></tr>
</table>
</form>
<?php
}
function isValidEmail($email){
$pattern = "^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$";
if (eregi($pattern, $email)){
return true;
}
else {
return false;
}
}
function sendMail($name,$email,$message){
$subject = "Message from website";
$from = "From: $name <$email>\r\nReply-To: $email\r\n";
$header = "MIME-Version: 1.0\r\n"."Content-type: text/html; charset=iso-8859-1\r\n";
$content = htmlspecialchars($message);
$content = wordwrap($content,70);
mail(MAIL_TARGET,$subject,$content,$from.$header);
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>Email form</title>
<link href="style/style.css" rel="stylesheet" type="text/css" />
</head>
<body background="/assets/images/GryPatBackD.gif">
<div id="main">
<div id="caption">Email</div>
<div id="icon"> </div>
<?php if (!isset($_POST['submitBtn'])) {
createForm();
} else {
$name = isset($_POST['name']) ? $_POST['name'] : "";
$email = isset($_POST['email']) ? $_POST['email'] : "";
$message = isset($_POST['message']) ? $_POST['message'] : "";
$usercode = isset($_POST['usercode']) ? $_POST['usercode'] : "";
$error = false;
if (strlen($name)<2) {
$error = true;
$error1 = errorName;
}
if (!isValidEmail($email)) {
$error = true;
$error2 = errorEmail;
}
if (strlen($message)<10) {
$error = true;
$error3 = errorMsg;
}
@session_start();
if ($_SESSION['AntiSpamImage'] != $_REQUEST['usercode']) {
$_SESSION['AntiSpamImage'] = rand(1,9999999);
$error = true;
$error4 = errorCode;
}
if ($error){
createForm($name,$email,$message,$error1,$error2,$ error3);
}
else {
sendMail($name,$email,$message);
?>
<div id="result">
<table width="100%">
<tr><td>
Your message has been sent!
</td></tr>
</table>
</div>
<?php
}
}
?>
<div>
</body>