Mailbag: Why does Windows Update continue offering the .NET Framework 3.5 SP1 after I install it?

Question:

I recently installed the .NET Framework 3.5 SP1 on my computer.  Afterwards, I went to the Windows Update site to check for updates, and I see the following item in the list of updates that my computer needs:

Microsoft .NET Framework 3.5 Service Pack 1 and .NET Framework 3.5 Family Update for .NET versions 2.0 through 3.5 (KB951847)

Does this mean that the .NET Framework 3.5 SP1 failed to install correctly when I installed it previously?  What do I do to fix this issue?

Answer:

No, this does not mean that the .NET Framework 3.5 SP1 failed to install correctly on your system.  Unfortunately, the wording of the name of this update in Windows Update is confusing.  The .NET Framework 3.5 Family Update is an additional hotfix package that needs to be installed after installing the .NET Framework 3.5 SP1.  Windows Update automatically bundles the .NET Framework 3.5 SP1 with the .NET Framework 3.5 Family Update if it detects that the .NET Framework 3.5 SP1 is not yet installed on your computer.  However, if the .NET Framework 3.5 SP1 is already installed on your computer, Windows Update will only install the .NET Framework 3.5 Family Update even though the name of the item includes “Microsoft .NET Framework 3.5 Service Pack 1” in it.

If your computer is in this state, you should be able to simply allow Windows Update to install the .NET Framework 3.5 Family Update on your system.

Additional troubleshooting steps in case the .NET Framework 3.5 Family Update fails to install

Note that if the .NET Framework 3.5 Family Update fails to install, there should be log files created on your computer to help narrow down the cause of the failure further.  They will be located in a sub-directory of your %temp% directory and have a folder name that includes the KB number of the .NET Framework 3.5 Family Update.  There are several possible KB numbers for the .NET Framework 3.5 Family Update:

  • KB958481
  • KB958483
  • KB958484