
Here's what you do.
1. Open a Command Prompt as Administrator
2. Type reg delete HKLM\SOFTWARE\Microsoft\SQMClient\Windows\DisabledSessions /va /f and press enter.
That's it. To open command prompt as an admin, you'll have to set the User Account Control slider to the lowest setting (Never notify), then reboot.2. Type reg delete HKLM\SOFTWARE\Microsoft\SQMClient\Windows\DisabledSessions /va /f and press enter.
After that, your MSI applications should install like normal. Coincidentally enough, even Office updates can't install when you're hit by this bug, since they're MSI-based. [Chris123NT via ZDNet]