WebForms.js or WebUIValidation.js CDN
In the console, it was giving me two errors saying it could not GET these two files from the CDN:
http://ajax.microsoft.com/ajax/4.0/2/WebForms.js
http://ajax.microsoft.com/ajax/4.0/2/WebUIValidation.js
To fix it, you need to delete the <script></script> references for both of the files above and make a single reference to:
<script src="http://ajax.aspnetcdn.com/ajax/4.5/6/WebFormsBundle.js" type="text/javascript"></script>