I have the same problem and getting in the Console as well:
"Failed to load resource: the server responded with a status of 404 (Not Found) - http://www.imagesnorth.com/modules/mod_s5_contact_popup/tmpl/ajax.php
even though the file is of course there.>
I tried CHMOD to 755 - no change.
If I remove the .htaccess and turn off URL rewriting, I get 500 Internal Server Error.