Member Rara Avis
I just logged in as you, Steve, and didn't have any trouble accessing the forums in MC. That suggests your settings on the server are fine.
I'm guessing your username and password are not properly set in your local cookies. You can check to see what cookies are currently set in the Member's Area, or alternatively, you can simply go into your Profile and click on the Submit button (you needn't change anything). Submitting your profile should set permanent cookies that can be read by the MC forums.
If that doesn't help and the problem persists, can you be more specific about "does not allow access"? What message, precisely, does it give you?