If you import all your users and groups across from vbulletin and have users in the banned users group, because of the permissions that group has applied to the forum of denied on all, the user is unable to navigate anywhere all they will get unless they try to log out is
You do not have permission to view this page or perform this action.
When you try to log out you get the You have been banned error.
If you take the user out of the Banned User's then you get the You have been banned error.
I guess the easiest way to resolve it would be to just delete the Banned Users group after you've imported it, however it might raise the question of whether the You have Been Banned message should over rule any other error message that is displayed (so a reordering of the check rather then permissions first to is banned first?)?