Shall we guess your full Windows version (e.g., Vista 64-bit SP1) or are you going to tell us? PS: If you think your Registry needs to be “cleaned” or “repaired” and you need more cluestick, read [link] and draw your own conclusions.

Polly, OK, now please provide some pertinent information so that someone *may* assist you: How to ask a question [link] Or, see this and resolve the error on your own: When you try to install an update for the .NET Framework 1.0, 1.1, 2.0, 3.0, or 3.5, you may receive Windows Update error code “0×643″ or