Here’s a tip for Virtual Server administrators: remember to remove the Virtual Server virtual machine (VM) additions before upgrading a guest VM’s operating system version!
I just upgraded a Windows Server 2003 VM from standard to enterprise edition and couldn’t get the mouse to connect (keyboard control was present, but not what you might call responsive). Virtual Server reported that the VM additions were not installed, but the guest still showed them as present in the Add/Remove Programs applet. Once they had been removed and then reinstalled, everything was back to normal.