Go here and download this batch of files and replace in your includes folder. That will update to compatibility with PHP 5.3.
I have the same problem - the web hosting has been updated to php5.3 and now my form submit is throwing an error, but the compatibilty patch has not made the slightest difference, I am still getting the following errors:
Warning: Parameter 2 to Trigger_Default_FormValidation() expected to be a reference, value given in /home/in2conf/public_html/includes/tng/tNG.class.php on line 228
Warning: Cannot modify header information - headers already sent by (output started at /home/in2conf/public_html/includes/tng/tNG.class.php:228) in/home/in2conf/public_html/includes/common/KT_functions.inc.php on line 464
Can anyone help please?