Two "structural" possibilities for this:
Either the call to the validate script is "misdirecting" (not pointing to the correct location in your directory) or
The validate script is not able to locate the form in the Spry panel and fails to validate.
The issue of blank submissions makes me think it's something else altogether though. Do they both run through the same script (ASP, PHP or CGI) to send the form?
If not you might want to look at the script for the Spry paneled form and see if it matches the other.