I'm using this plugin on this site: http://www.partyhiredirect.com.au/ One of the forms can be seen is on this page: http://www.partyhiredirect.com.au/party-hire-direct-site-under-construction/new-supplier-listing-form/
I have 6 different FS forms on the site, and some of them are used on multiple pages.
When a user submits the form incorrectly (ie: leaves a required field blank), rather than displaying the error messages the form redirects to "page not found". This is happening on all 6 forms. They were working fine up until now.
I have done the following:
1. Uninstalled the theme and tested the form using another theme
2. Deactivated all plugins
3. Increased PHP memory limit to 256M
4. Set debug on wp-config to "true" (no error messages)
5. Uninstalled and reinstalled the contact form plugin
6. Deleted all forms except for one.
None of this made a difference.
My last resort is to try a different form plugin, but would appreciate any other suggestions before I take that route.