TechTips – Vista Error Code 646 Can’t Install Windows Updates
I have seen this error so many times it drives me crazy, mainly because it’s a program flaw in Vista and I have heard some people have had the same issue with Windows 7. I haven’t seen it with any of my Windows 7 boxes but plenty of Vista boxes. Basically what is happening is your machine says it has updates, when you try to install them you get this error.
“Error Code 646, Windows Update encountered an unknown error”
I would like to thanks Microsoft for this awesome error code description that gives so many details to what is going on. I was pulling my hair out trying to figure out why this was happening and why I was getting error code 646. I tried many different things that I thought might be causing the problem.
Disabling Anti-virus
Disabling firewall (windows and my Antivirus firewall)
Tried to manually download the files and install them (didn’t work gave me the same error)
Tried the Microsoft Patch Registration tool (didn’t work)
Tried System restore (my system restored to an older state but the updates still won’t install)
After trying all of these supposed fixes I was ready to quit and just ignore the updates. The only problem with ignoring the updates is that I wouldn’t get future updates and we all know Windows needs updates. The updated not only make it run smoother (although sometimes updates make it worse) but the updates often contain really important security patches. With all the viruses out there today I want my PC as up to date as possible and with as few holes as possible.
So finally I decided maybe it was a permissions issue that was stopping the updates, which doesn’t make sense since it’s a Microsoft built-in feature (Windows Update that is) and should be allowed to install as it wishes. So just on a whim I decided to turn off the UAC (User Account Control), you probably know what this is, it’s the annoying pop -up that says “Are you sure you want to allow” every time you want to install something in Vista or Windows 7.
Well I couldn’t believe it but after I turned off UAC and rebooted, I tried to install the updates and they installed with no problems! I at first thought that maybe something else I had done previously just started working but I have since done this to several other machines with the same problem and the only thing I had to do on them was disable UAC. All of them have updated perfectly once the UAC was off.
So to turn off your UAC do the following:
1. Click Start
2. Click Control Panel
3. Double Click User Accounts
4. Choose the account you are using
5. Click the Turn user account Control On or Off
6. Uncheck the box that says “Use User Account Control (UAC) to help protect your computer)
7. Click OK
8. Reboot
9. Install patches (it should work)
10. Reverse the steps above to turn UAC back on, so you are protected again
11. You are done!
If those instructions weren’t clear enough you can check Microsoft’s website here it show you how to do it.
It took me a long time to find a work around for this bug, who would have thought that the built in security control would stop Microsoft from updating its own software. I guess the protection is working if it won’t even allow Microsoft to make changes to the OS without me turning the UAC off. Hope this solves your problems with the Error code 646 and having issues installing updates.
Sources
Microsoft Support “Description of the Patch Registration Cleanup Tool” Microsoft
Microsoft Support “Turn User Account Control on or off” Microsoft
Microsoft Support “Download details: Windows Installer 4.5″ Microsoft
