I have had two different vCenter 5.5 servers (on Windows 2008 R2) over the course of three months that have suddenly decided to ignore AD groups when allowing users to access resources, locking everyone out who does not explicitly have permissions (including the local Administrators group, thankfully I was able to log in as administrator@vsphere.local and give myself explicit permissions) and for the life of me I cannot find any hint on what could cause this. As far as I am aware, no system changes were made and no software updates applied to either Windows or vCenter. In the first case we gave up and built a whole new vCenter after a day of trying to troubleshoot, as we were going to move to 6.0 anyway so I can't get logs or anything and in the second since it is a small deployment we were able to just give everyone explicit permissions instead of using their AD groups. This is a system that i'm helping someone else troubleshoot, but I should be able to get logs if need be.
Has anyone else run into this?