500 server error with add group admin button on IIS, PHPRunner 10.6

I'm getting the following error trying add a group on my site (admin_rights_list.php). I am running IIS. I've duplicated another site hosted on the same server and it works just fine. I'm wondering is this a permission issue or some setting I'm missing. Any help is appreciated. Thanks

Server Error

500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed.