I'm not sure how Formidable Pro works, so I may not be able to help here.
I would recommend that you check for Javascript errors when submitting the form, and let me know if you see any errors related to my plugin.
You can find out how to enable the Javascript console here:
http://webmasters.stackexchange.com/questions/8525/how-to-open-the-javascript-console-in-different-browsers
