It appears to be an error in the php code when the form is submitted. I can't debug it directly without FTP access, but you could try adding this to the top of the page:
<?php
ini_set('display_errors',1);
?>
That should at least give you an error message instead of a blank page and may lead you to the solution.
If you still need help you can post FTP information and I can help you debug it.