Same issue here as well - has anyone come up with a fix?
I had an SEP 11 RU7 install on a Windows SBS 2008 LAN - worked fine - all clients got updates daily.
Upgraded SEPM to 12.1, then exported and linked new 12.1 client installers to the groups.
Workstations successfully upgraded to 12.1, but since initial upgrade, most have not updated any of the definitions. Only one machine (the last remaining Windows XP x86 workstation) continues to update - and it has not been rebooted since the update.
All workstations that do not update are either Vista x86 or Windows 7 x64.
I have tried turning off UAC and manually reinstalling the client on a couple of workstations, but no updates ever get installed. I see a message in the System Log each day stating that http://SERVER1:2967/...../full.zip could not be downloaded.
Any help would be much appreciated!