When I try to install .NET Framework 3.5 on Windows Vista 64bit Home Premium edition it did not work. The Windows Update error code was 643. How do I fix this problem and install it?


The first thing to try is to remove all instances of the .NET Framework and see if it installs after that. There is a tool for doing this: .NET cleanup tool . Restart your computer and try to install it again. If this does not work, you will need to do an in place reinstall. Get our your reinstall DVD and follow the instructions to do a reinstall. DO NOT do a full reinstall and lose all your program files and drivers, just do an in place reinstall. After the reinstall finished, I was able to install the .NET Framework.

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    Stebner's .NET cleanup tool is excellent, got me out of a rather tricky situation with a production server that completely messed up after .NET 3.5SP1 flunked out during installation. +1 – Kev May 1 '09 at 16:06

There are some instructions on a workaround in a knowledge base article 923100 about the error code 0x643 that may show up when installing .NET.

The gist of the solution is that you need to uninstall .NET and install it again. I hope the kb helps you out.

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  • This is a good first thing to try. In my case, this didn't solve my problem and I had to do an in-place reinstall. – RyanTM Apr 30 '09 at 23:05

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