error when posting on group forum: You don't have permission to access

I don't know if the Buddy Avtivity Plus is the issue (seems to be working)

Noticed after positing on Group Forums:

You don't have permission to access / Additionally a 500 Internal Server error was encountered while trying to use an ErrorDocumetn to handle the request.

- Although the Topic comments do indeed post despite the error.
I called the hosting service (goDaddy -client's choice) They say it is a plug in or permalink issue.

I did activate and reactive bbPress after my SiteWide Forum install worked then mysteriously stopped working. I deleted the links to the new Forum and Topics etc.
Ultimately I switched to Group Forums as it seems more stable. ? I did delete some of the Topic comments before reinstalling bbPress.

Any help is greatly appreciated. It may be a bbPress config issue per research I've done online.

Thanks