This one is easy to explain, but so far hard to fix. My systems are all set up to allow Remote Desktop Protocol (RDP) access. Most of the clients connect from home, and I can do updates and fix issues after hours without using up more Gasoline. This has worked fine until SP3. After install of SP3 I can no longer use RDP. A rollback to pre SP3 and I can get back on. Add SP3, and again, no RDP.
I tried a chat session with MS. When I asked the tech "I can no longer connect via RDP to my machine after installation of SP3, can you tell me why?" His informed answer was, "Most likely because of registry changes made by SP3." Gee...Ya Think?
A packet sniff (wire shark) of the system shows that it receives the RDP request, it just doesn't seem to respond to it.