When you try to do checkpermissions for a user added on thesite through AD group you get “none” even though group has permissions on thesite and user also doesn’t have any issue in logging into the site. It’s justthat the check permission doesn’t work for the group and the user.
Take a ULS while doing check permissions and if you see thefollowing entry
04/02/201217:27:49.89 w3wp.exe(0x169C) 0x0974 SharePointFoundation General 7fdb Unexpected AuthZInitializeContextFromSidfailed! ddd8bfd7-3a2d-4b94-8249-0e22f057a52f
This comes if the farm account doesn’t have permissions toread the TGGAU attribute of the group or the user ID. To resolve this login toyour Active Directory
And that should be it J.
For details about the TGGAU attribute refer http://support.microsoft.com/kb/331951
Are there any other prerequisites? I've added my farm and app pool account to this AD group but I still cannot check permissions on individual users.