Form Validation Problem in IE7

onsubmit doesn't work properly?

[MinistryOfTruth]

OK, I have this:

<script type="text/javascript">
//<![CDATA[
String.prototype.trim = function(){return this.replace(/^\s+¦\s+$/g,'')}
var regEmail = /^[a-z0-9][a-z0-9_\.-]+@[a-z0-9_\.-]+\./i;

function validate(form)
{
var errMessages=[];
if (form.email.value!="")
{if (! regEmail.test( form.email.value.trim()))
errMessages.push("Please enter a valid email Address.");
}
var valid =!errMessages.length;

if(!valid)
alert(errMessages.join("\n"));
return valid;
}
//]]>
</script>

and then

<form action="contact.php" method="post" id="cForm" onsubmit="return validate(this);" >
<p>
<label id="textfield" for="posEmail">E-mail:</label>
<input class="text" type="text" size="25" name="email" />
</p>
<input class="submit" src="images/signup.jpg" type="image" name="Submit" id="sendContactEmail" />
</form>

It works in everything but IE7. There, the form can't be submitted at all. Nothing happens when you press the submit button or press enter in the form.

Can anyone help work out what's going wrong?

[RonPK]

It works fine in my IE7.