Use this solution here: http://forum.ait-pro.com/forums/topic/digital-access-pass-dap-fix/#post-6904 and also add the additional DAP “signup_submit.php” filename. This is not all of the solution code that is in the link above and is only an example below to show you where to add the additional DAP “signup_submit.php” filename.
# Example: Whitelist additional misc files: (example\.php|another-file\.php|phpthumb\.php|thumb\.php|thumbs\.php) RewriteCond %{REQUEST_URI} (authenticate\.php|signup_submit\.php|timthumb\.php|phpthumb\.php|thumb\.php|thumbs\.php) [NC]