I just upgraded a new SBS 2011 Std to SP1 and Exchange 2010 to SP2 today and ran the PSConfig update successfully for SharePoint. I ran a manual Backup successfully afterwards and a scheduled backup ran at the correct time later. When I check various folder's properties for Previous Versions, there are none available. VSS starts but goes idle according to application event logs, according to blogs, this is a benign error. The Volume Shadow Copy service is started but set to Manual. I have rebooted a couple of times since the PSConfig update.
Will Previous Versions resume functioning after a period of time?