Error codes "0x8007066A" or "66A" occur when you install the .NET Framework updates

When you try to install updates for the .NET Framework by using Windows Update or Microsoft Update, you may receive an error that has one of the following error codes:

• error code 0x8007066A
• error code 66A

Note If you are not installing the .NET Framework Updates when you receive error code 0x8007066A, go to the following article for troubleshooting steps:

This problem can be caused by system corruption on your computer. This may occur for various reasons, including but not limited to corrupted hard disk sectors or another application overwriting the .NET files.

To troubleshoot this issue, follow the steps in these methods, starting with method 1.

Method 1: Repair the .NET Framework 4 installation

Follow these steps if you are running Windows Vista or Windows 7:

1. Close all 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.

Follow these steps if you are running Windows XP:

1. Close all programs.
2. Click Start, click Control Panel, and then click Add 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 the issue is not resolved, go to method 2.

Method 2: Fix MSI software update registration corruption issues

To fix MSI software update registration corruption issues, run the automated Fix it tool in article 971187 in the Microsoft Knowledge Base.

After you run the Fix it tool, click Start, click AllPrograms, and then click Windows Update. Try to install the updates again.

If the issue is not resolved, go to method 3.

Method 3: Manually download and install the update

To manually download and install 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 based on your version of Windows:
3. • 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.
4. In the list of updates, find the update that contains the error message, and note the Knowledge Base (KB) article number for the update that you want to install.
5. Go to the Windows Downloads
   (http://www.microsoft.com/download/)
   website.
6. In the Search Download Center box at the top of the page, type KB and then type the article number for the update.
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7. Press Enter or click the search icon.
   
   For example, if the KB article number that is 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).
8. In the Search Results list, locate the KB article that you searched for, and then go to that article.
9. Click Download, and then click Save in the File Download dialog box.
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10. In the Save in list, click Desktop, and then click Save.
11. On your desktop, locate the file that you downloaded, and then double-click the file to install the update.

Note If the update is unsuitable for your computer, the installation may still fail.

Method 4: Repair 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. To download the tool, go to the following MSDN blog post:
   .NET Framework Cleanup Tool User's Guide

   (http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx)
2. After the download is complete, click View downloads.
   
   
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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 Product to cleanup, 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:
   http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3
   (http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3)
   
   
   The .NET Framework 1.1 SP1:
   http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en
   (http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en)
   
   
   The NET Framework 3.5 SP1 (this also installs the.NET Framework 2.0 SP2 and the .NET Framework 3.0 SP2)
   http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en
   (http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en)
   
   
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 about the .NET Framework Cleanup Tool, go to the .NET Framework Cleanup Tool User's Guide blog post.

More information:

If these steps did not resolve your issue, you may need to collect additional logging information to troubleshoot your issue. To do this, follow the steps in the following Microsoft Knowledgebase article:

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