.NET Framework 1.1 SP1
I had trouble installing the Windows Update for the .NET Framework 1.1 SP1. If you have similar problems, uninstall the .NET Framework 1.1 SDK. I think there was an update or “hotfix” to the SDK at some point, which the 1.1 SP1 redistributable complained about.
Once I removed the SDK, I was able to re-install the 1.1 SP1 with no problems.