As per forum thread: http://forums.formtools.org/showthread.php?tid=2999

and as requested by Joe

I had code in the hooks manager for 'ft_update_submission, start' and 'end'. When ft_update_submission was called by edit_submission.php thus
[code]list($g_success, $g_message) = ft_update_submission($form_id, $submission_id, $request);[/code]
the variables $g_success and $g_message were being returned as NULLs. This then resulted in the $failed_validation being true. This was irrespective of the failure or success of my code.

Now although my code was actually working, there are two override variables in the hook manager... $success and $message which I was not manipulating. They were defaulting to NULL.