[Rtir] RT-4.2.1 and RTIT 3.0.0

[Niall]

I have install RT 4.2.1 and it works ok. Then I installed RTIT 3.0.0 but now 
the web pages to login to the admin console will not load.

The error i get is: "the server encountered an internal error or 
misconfiguration and was unable to complete your request"

If I remove the RTIT plugin from TR_SiteConfig.pm the web page will load. 

Does anyone have any idea how I can identify what is causing this to fail