Did you logoff and log back on? The groups in your security token are populated when you logon.
Reboots and re-logins have no effect. I can assign an old group (containing me) to a folder and it gives me permissions immediately as you'd expect. If I do the same with a new group there is no effect. I checked I am making Global Security groups, not some other type. I'm creating the groups the same way I did weeks ago. This problem is also tricky because I can't yet find any Google search word combinations that give useful results. Greg