.NET Framework update installation error: "0x80070643" or "0x643"

1. To fix MSI software update registration corruption issues automatically, click the Fix it button or link, and then click Run in the View Download dialog box. Then, follow the steps in the Fix it wizard.
   Note: This Fix it does not apply to Windows 8 or Windows RT.
   
   
   Fix this problem
   Microsoft Fix it 50123
   
   
   
   
   Note This wizard may be in English only, but the automatic fix also works for other language versions of Windows. If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD or DVD, and then run it on the computer that has the problem.
   
   For more information about how to fix this issue, see How to fix MSI software update registration corruption issues.
2. Visit Windows Update, and then try to install the updates again. Or, update Microsoft Security Essentials.
3. Try to reinstall the .NET Framework update.

If the issue is not resolved, go to method 2.

Download the Microsoft .NET Framework Repair Tool to repair the following versions of the .NET Framework, and then reinstall the .NET Framework update:

• The .NET Framework 4
• The .NET Framework 3.5 SP1
• The .NET Framework 3.0 SP2
• The .NET Framework 2.0 SP2

For more information, see Version 2 of the Microsoft .NET Framework repair tool is available. If the issue is not resolved, or if you are using other versions of the .NET Framework, go to method 3.

Use the .NET Framework Cleanup Tool to uninstall multiple versions of the .NET Framework, and then reinstall the components.

To do this, follow these steps:

1. Check out the .NET Framework Cleanup Tool User's Guide.
2. Download the .NET Framework cleanup tool.
3. When you are prompted, click Open, and then click Extract Now.
4. In the files that you extracted, double-click cleanup_tool.exe.
   If you are prompted for an administrator password or for confirmation, provide the password, and then click Continue.
5. In the Do you want to run the .NET Framework Setup Cleanup Utility? message, click Yes.
6. Click Yes to accept the license agreement.
7. In the Product to cleanup window, click the list, select .NET Framework - All Versions, and then click Cleanup Now.
   Note The cleanup tool does not let you remove the .NET Framework 2.0 in Windows Vista or later versions of Windows because the .NET Framework is installed as an operating system component.
8. After the .NET Framework is removed, restart the computer.
9. Download and install the following components:
   The .NET Framework 1.1
   
   The .NET Framework 1.1 Service Pack 1 (SP1)
   
   The .NET Framework 3.5 Service Pack 1 (this will also install the .NET Framework 2.0 SP2 and the .NET Framework 3.0 SP2)
10. Restart the computer.
11. Visit Windows Update again, and then check for and install updates.
12. Try to reinstall the .NET Framework update.

You may also experience the following issues when you install .NET Framework updates:

• The update is not installed.
• The system keeps reminding you to install this update even though you have already installed it.
• The desktop does not appear.

If you experience one of these issues, try the following methods to resolve the issue.

Method 1: Reset Windows Update components and update your computer

To reset the Windows Update components automatically, click the Fix it button or link, and then click Run in the View Download dialog box. Then, follow the steps in the Fix it wizard.

Note This Fix it Solution has two modes: Default and Aggressive. You should run the Fix it solution in Default mode to see whether it resolves your problem with Windows Update before you run it in Aggressive mode.

Fix this problem
Microsoft Fix it Microsoft Fix it 50202

Note This wizard may be in English only, but the automatic fix also works for other language versions of Windows. If you are not on the computer that has the problem, save the Fix it solution to a flash drive or a CD or DVD, and then run it on the computer that has the problem.

For more information about how to reset Windows Update components, see the following article:

Method 2: Manually download the update from the download link and install it in clean boot mode

We suggest that you install the updates in clean boot mode to avoid interrupting non-Microsoft programs. To enter clean boot mode on a computer, follow these steps:

1. Click the Start button, type msconfig in the Start Search box, and then press Enter. If you are running Windows 8 or Windows 8.1, type msconfig on the Start screen, and then press Enter.
2. If you are prompted for an administrator password or for confirmation, type the password or click Continue.
3. On the General tab, click Selective Startup.
4. Under Selective Startup, clear the Load Startup Items check box.
5. Click the Services tab, click to select the Hide All Microsoft Services check box, and then click Disable All.
6. Click OK.
7. When you are prompted, click Restart.
8. After your computer restarts, try to update your computer again.

For more information about this method, see the following article in the Microsoft Knowledge Base: