Which one you are using? Also if you creating lead using Munchkin API then also Marketo will not create new lead if email address and domain is same. Check the sample code below.
<head>
<title>Page 1</title>
<script src="http://munchkin.marketo.net/munchkin.js" type="text/javascript"></script>
<script>Munchkin.init('########');</script>
<script type="text/javascript">
function MarketoUpdate() {
alert("inside fun");
Munchkin.munchkinFunction('associateLead',{
Email: 'hg@yahoo.com',
FirstName: 'Gupta',
LastName: 'Harish' },
'f5ed2b4d167306155ee4aaa3f606bbef5691a3cc');
alert("ret fun");
}
function clickLink2(){
alert("in click");
Munchkin.munchkinFunction('clickLink', {
href: '/MyFlashMovie/Story1'}
);
}
</script></head>
<body>
<form name="form1" onsubmit="MarketoUpdate()">
<input type="submit" value="Submit"/>
</form>
<a href="page2.html" onclick="clickLink2();">Link to page 2</a>
</body>
</html>