I checked for updates this morning and 6 were available, 3 important and 3 optional. All were security fixes for .Net 4 and all failed with an error code of 2, which basically shrugs it's shoulders and says "dunno". Tried a couple of times and spent a fair amount of time Binging.

Tried again this evening and there were 13 updates, 6 important and 7 optional, all still .Net 4. Aha says I. They found the problem. Now I have seven failures instead of 6.

When I retry, it doesn't re-download, but just keeps reinstalling the failed files and I got to wondering if that could be the trouble. Does anyone know a way to delete the failing updates? A search shows the KB files in the Users\Appdata folder, but even though I have full control of Users, Appdata doesn't appear.

C:\Windows\SoftwareDistribution\Download

that's your Windows Update cached downloads folder. Delete everything in it and try again.

Appdata is a Hidden folder, so make sure you have hidden files/folders visible.

For Windows Update, sometimes you need to install them one at a time, especially for security patches.

Nope. Still failing, even one at a time. BTW DEFRON, emptying that folder periodically is probably a good idea anyway. I think it had about a GB in there. I guess I'll just wait a few days and see if something shows up in MS's forums. If not, I'll just hide the damn things and go on with my life.

Have you seen http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_update/windows-update-error-code-2-trying-to-install/ee945c20-a8c1-4b82-9b4c-d6dfae4c5337? It could be that there's something mucked up with your current installation of the framework. If I were you I might try removing that version of the framework altogether and reinstalling it.