Windows Update: Fix error 643

If you want to update Windows, error 643 can occur, so that the update no longer works. In this article, we'll explain what the error code means and how to fix it.

Solution 1: Fix Windows Update error 643 via Fix-It

Error 643 or 0x643 indicates that the MSI software update registration or the .NET Framework installation is faulty. The problem therefore mainly occurs when you want to download an update for the Microsoft .NET Framework. With a Fix-It for Windows 7 you can get a grip on the problem quickly. Windows 8 and 10 users need to do it differently, as we'll show in the next section.

1. Download the free Fix-It from Microsoft and run the file.
2. Check "Agree" to accept the license terms.
3. Then click on "Next" and confirm the security prompt of the user account control with "Yes".
4. After the repair process is complete, you can close the tool again. Then start Windows Update again.

Solution 2: Fix error 643 in the .NET Framework

If you were unable to fix the problem with the first method, you need to repair the .NET Framework:

1. Download the free "Microsoft .NET Framework Repair Tool" and start it.
2. Confirm that you have read the license agreement and click "Next".
3. After analysis, the tool suggests changes that could fix the problem. Confirm this suggestion by clicking on "Next".
4. Leave the repair tool open and try to install Windows Update again. If the update was successful, you can close the tool. Otherwise, click on "Next" once more and follow the instructions given by the wizard.

Solution 3: Reinstall the .NET Framework and fix Windows Update errors

If the error persists, you can completely uninstall the .NET Framework and set it up again. Microsoft offers a special tool for this:

1. Download the ".NET Framework Setup Cleanup Utility". Unzip the archive into any directory and start the "cleanup_tool.exe" file.
2. Click "Yes" to confirm the start of the program. Then confirm the license agreement.
3. In the "Product to cleanup" drop-down list, select ".NET Framework - All Versions". Then click on "Cleanup Now".
4. Wait for the process to finish and then restart your computer.
5. Now download ".NET Framework 1.1" and install it.
6. Then download the ".NET Framework 1.1 Service Pack" and start the installation here.
7. Finally install the ".NET Framework 3.5 Service Pack 1" on your computer.
8. Restart your PC and run Windows Update again.

In our next practical tip, we will explain what to do if Widows Update stops working at all.