Have you modified the script any? And what version of PHP are you using? Does it happen on all data or just specific sets? Is this a new install or was it working previously?
Off the top of my head, I can think of a couple of things that could cause this, but it's hard to say for sure without having more info.
My first thought was some special character in the data that's breaking the validation, possibly in the email address.
Another idea, which is more likely if this was a previously working install of osTicket, was a corrupted database table, thereby causing the help topic info to be read incorrectly (and so the form gets populated incorrectly).
In order to help sort this out, you should turn on error reporting in main.inc.php
Change lines 44 and 45 from
ini_set('display_errors',0);
ini_set('display_startup_errors',0);
To
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
If you are running 5.3 you will probably get a couple of deprecation warnings when you do this (I think the pass-by-reference syntax has changed, etc.). Technically, these shouldn't be an issue. The script should still execute as desired and the error would get silently logged, but I've seen deprecation warnings bring things to a screeching halt before, depending on your server setup.
If that seems to be the case, you can try disabling them. (osTicket doesn't disable error reporting/logging, it simply disables them from being shown in the browser).
To do that, open main.inc.php again and change line 42 from
error_reporting(E_ALL ^ E_NOTICE)
to
error_reporting(E_ALL ^ E_NOTICE ^ E_DEPRECATED)
Note: only do this if you're running 5.3.0, since the E_DEPRECATED directive didn't exist prior to this version.
