Put the jQuery script tag before the script tag for validation
I just encountered this extremely frustrating error and lost the better part of an hour to it, for lack of a workable answer online. I confirmed in Firebug that I was hitting the CDN for both jQuery and validation.
In the end, changing this:
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.7/jquery.validate.min.js"></script>
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.4.4.min.js"></script>
to this:
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.4.4.min.js"></script>
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.7/jquery.validate.min.js"></script>
was all I needed.