"0x8007066A" or "66A" error when you install .NET Framework updates

One of the following methods frequently resolves this problem. Try these methods in the order in which they�re presented.

Method 1: Repair the .NET Framework 4 installation

If you run Windows Vista or Windows 7, follow these steps:

1. Exit all running programs.
2. Click Start, type Uninstall in the Search box, and then click Uninstall a program.
3. Double-click Microsoft .NET Framework 4 Client Profile.
4. Select Repair .NET Framework 4 Client Profile to its original state, and then click Next.
5. When the repair is complete, click Finish.
6. Click Restart Now to restart your computer.
7. To install the latest Windows updates, click Start, click All Programs, and then click Windows Update.

If you run Windows XP, follow these steps:

1. Exit all running programs.
2. Click Start, click Control Panel, and then click Add or Remove Programs.
3. Click Microsoft .NET Framework 4 Client Profile in the list of installed applications, and then click Change\Remove.
4. Select Repair .NET Framework 4 Client Profile to its original state, and then click Next.
5. When the repair is complete, click Finish.
6. Click Restart Now to restart your computer.
7. After you log on to Windows, click Start, click All Programs, click Windows Updates, and then click Check for updates.
8. When the scan is complete, click Install Windows Updates, and then follow the instructions.

If Method 1 does not resolve the issue, try Method 2.

Method 2: Fix MSI software update registry corruption issues

You may receive one of these error codes if the registry is corrupted. To fix this issue automatically, click�Learn More in the �Resolution� section of How to fix MSI software update registration corruption issues.

After you run the Fix it tool, click Start, click All Programs, and then click Windows Update and try to install the updates again.

If Method 2 does not resolve the issue, go on to Method 3.

Method 3: Manually download and install the update

To manually download and install the updates, follow these steps:

1. Click Start, click All Programs, and then click Windows Update or Microsoft Update.
2. To view your update history, do one of the following, depending on your version of Windows:
   • If you are running Windows XP, click Review your update history in the left pane of Control Panel.
   • If you are running Windows Vista or Windows 7, click View update history in the left pane of Control Panel.
3. In the list of updates, find the update that contains the error code, and note the Knowledge Base (KB) article number for the update that you want to install.
4. Go to Windows Downloads.
5. In the Search Download Center box at the top of the page, type KB and then type the article number for the update.
   
   
   
   
   
6. Press Enter, or click the search icon.
   
   For example, if the KB article number that�s listed for the update is 123456, type KB123456 in the search box, and then press Enter, or click the search icon. (The search icon looks like a white magnifying glass on an orange square.)
   
   
7. In the Search Results list, locate the KB article that you searched for, and then go to that article.
8. Click Download, and then click Save in the File Download dialog box.
   
   
   
   
   
9. In the Save in list, click Desktop, and then click Save.
10. On your desktop, locate the file that you downloaded, and then double-click the file to install the update.

Note If the update is not needed for your computer, the update will not be installed. If the update still fails with one of the error codes, try Method 4.

Method 4: Reinstall the .NET Framework

To repair the .NET Framework, you must first uninstall multiple versions of the .NET Framework by using the .NET Framework Cleanup Tool. Then, reinstall the components.

To do this, follow these steps:

1. Download the tool from the .NET Framework Cleanup Tool User's Guide.
2. After the download is complete, click View downloads.
   
   
   
   
   
3. In the Downloads folder, right-click dotnetfx_cleanup_tool.zip, click Extract all, and then click Extract.
4. In the list of files that you extracted, double-click cleanup_tool.exe.
   
   Note If you are prompted for an administrator password or for confirmation, provide the password or confirmation, or click Continue.
   
   
5. In the Do you want to run the .NET Framework Setup Cleanup Utility message, click Yes.
   
   Note This tool may be in English only, but it also works for other language versions of Windows.
   
   
6. Click Yes to accept the license agreement, and then wait for the .NET Framework Cleanup Tool to start.
7. In the Product to cleanup 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 SP1
   • The NET Framework 3.5 SP1 (this also installs the.NET Framework 2.0 SP2 and the .NET Framework 3.0 SP2)
10. Shut down and then restart your computer.
11. Click Start, click All Programs, click Windows Update, and then try to install the updates again.

For more information, see the .NET Framework Cleanup Tool User's Guide blog post.

This problem may be caused by system corruption on your computer. For example, your computer may have corrupted hard disk sectors, or an application may have overwritten the .NET Framework files.

If this problem is still not resolved, you may have to collect additional logging information so that Microsoft Support can help you troubleshoot the problem. To collect the logging information, follow the steps at How to Enable Microsoft Installer logging and verbose logging to gather additional troubleshooting information before you contact Microsoft Support.

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