Do you have any error logs? It could be that it's just logging the error to the server error logs?

It almost looks like you might have some sort of php issue going on. I'm getting a blank (empty) page, even if I type a bogus URL that has a php extension:

http://server2.termpro.com/forums/booboo.php - results in a blank page

http://server2.termpro.com/forums/booboo.html - results in the proper page not found error