When accessing the Windows Update website on Windows 2000, XP, or Server 2003, you can sometimes get an error which tells you nothing other than "a problem occurred" and an error code:
0x800B0001
This is virtually useless for troubleshooting, of course.
Microsoft does have a solution to this, which involves lots of command line typing to re-register various .dll files that have become unregistered for some reason.
It works, but it is error prone and annoying.
This script download should make things somewhat easier, as it automates the entire process, with the exception of the success/failure messages for each .dll registration. These are simply messages that say whether the registration worked, and you click "OK" on each one.