hcl-2. 1. 7 on unix

I run index. php and it gets to hxxp: www. domain. info/hcl/module. php?module=HelpCenter and then produces and error.

"Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request "

I traced the error to this following line,

in module. php
$GLOBALS['template']->display('mod_'. addslashes($_GET['module']). '. tpl');


What's installed:
Apache 2. 2. 13   Running
MySQL 5. 0. 67
PHP Version 5. 2. 10

How can I fix this?