Reply #3: I have seen this a number of times

[Egnever]

There are sometimes ways to work around it by deleting the folder where updates are downloaded to and then retrying the download, another way is to manually download the update and install it yourself. Having said that those only work rarely. I have found the most sure fire way to fix this issue is to uninstall all .net and rebuild from scratch. there is a utility that helps get this done fairly quickly.

You can find a write up on it and download link here http://blogs.msdn.com/b/astebner/archive/2005/04/08/406671.aspx