1. Please re-upload the /include/client/viewticket.inc.php from the distribution package. It sounds like something got messed up with it.
If that doesn't fix it move on to 2.
2. Please check your php.log for error messages. The location of this file varies by php install (and OS) as well as if your running your own server vs hosted solution. If you have access to your php.ini you should be able to look up its location there.
If you do not have access to the logs or the php.ini you can turn on error reporting to the screen. To do this follow these directions:
locate and edit the /main.inc.php
On about line 43 locate
#Don't display errors
ini_set('display_errors',0);
ini_set('display_startup_errors',0);
and change it to:
#Don't display errors
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
To shut them back off again later simply change the 1's back to 0's. Please report any errors you get here if you need help interpreting them.
Good luck!