What Is Windows Update Error 66a?

If your computer is in the process of performing a Windows update and you get an error code 66a, it’s most likely a Windows firewall issue that will prevent you from completing your system update. If your system can’t install updates, you’re at risk for all sorts of viruses and malware, data loss, and system instability.

What Causes Windows Update Error 66a?

One cause for this error is having damaged registry files. You may also get this error code if you start your computer in safe mode. Essentially, your system discovered corrupted files that are preventing a system driver from updating the Microsoft .NET Framework 4 Client Profile.

How to Fix Windows Update Error 66a

Solution 1: Fix your .NET Framework installation

Steps :

1. Begin by closing any programs your computer is running.
2. Click your Start button.
3. Click your Control Panel button.
4. Go to Programs.
5. Click the Uninstall a Program button.
6. Double click on the Microsoft .NET 4 Client Profile program.
7. Choose the Repair option.
8. Click the Next button. Your repair will begin automatically then, and may take several minutes to complete.
9. Click the Finish button.
10. Click the Restart Now button. You must restart your computer for the repair to complete.
11. After your computer restarts, the Windows Update and try installing the update.

Solution 2: Download update and install it manually

Steps :

1. Go to Microsoft’s Search page: http://search.microsoft.com
2. Enter this  in the knowledge base search box: 66a kb
3. Look through the list of search results to find an article that contains a link to download the package your system needs.
4. You may need to validate Windows before you can complete the download.
5. Click Download.
6. Click Save.
7. Click Desktop.
8. Click Save again.
9. Go to your Desktop.
10. Double click the file you downloaded to begin the installation. Follow the instructions on the screen to complete the installation. This may take several minutes.

Most likely one of these solutions will work for you, but if not, your .NET Framework may need to be repaired before you can install the updates your system needs.

Solution 3: Repair your .NET Framework first, then install any updates your computer needs.

Steps :

1. Use Microsoft’s .NET Framework Cleanup Tool. You can find it here: http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx
2. Run the tool.Select the required .net framework and remove it.Then restart your computer.
   
3. Reinstall three components your computer needs to run properly. Click on these links to get them.

.Net Framework 1.1:
http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=262d25e3-f589-4842-8157-034d1e7cf3a3

.Net Framework 1.1 SP1:
http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en

.NET Framework 3.5 SP1
http://www.microsoft.com/downloads/details.aspx?familyid=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en

4. Restart your computer.
5. Go to the Microsoft Update page: http://update.microsoft.com
6. Install any updates your system needs.

Hope this solve the error.Good Luck.