Is your Windows 10 Update failing with error code 0xC1900101 (or 1900xxx)? I may have a solution.

For months--and I do mean literally months--I had the issue that Fast Track Insider builds stopped updating. It would appear to be working until a message on the black update screen stated that the update had failed, and Windows was rolling back to the pre-update build.

After trying a ton of what turned out to be useless suggestions I decided I needed to do something so I could get beyond spinning my wheels trying to resolve this, even if it meant losing settings. So a few weeks ago I backed everything up and did a clean install where I mounted a recent ISO build (I believe it was 19013), choosing to keep my files. 

I lost a lot of my settings, but it worked--my PC was finally updated, though I had to reinstall a bunch of stuff, which was time-consuming and work intensive.

After a couple of subsequent successful updates I thought I was finally in the clear. That is, until IT STARTED HAPPENING AGAIN, for build 19041--this time instead of getting a rollback message when the PC rebooted to complete the install (as it had every time before my clean install to 19013) the hourglass would spin on the opening Dell screen for literally hours. I got fed up and had to perform a hard shutdown and then restart, and I had to do this more than once just to get to the logon screen. After I was finally able to boot to find that I was still on the un-updated Windows 10 build I checked Windows Update history, and saw the message in Settings advising there was a problem listing error code 1900xxx, and maybe research the reason and to try again later. So I did try again later--to the same results. And this pattern happened literally very single time I tried to do this. 

And guess what--it worked. My PC was finally updated. Immediately upon rebooting to the newest insider build (Windows 10 Insider Preview 19041.1) the first thing I did was go to Windows security settings, and real-time monitoring was turned back on--Windows Update did that, as while it was updating I obviously had no access to the PC.

So the next time an update was available (Windows 10 Insider Preview 19536.1000) I decided to NOT turn off the Windows real-time anti-virus protection and see what would happen--maybe the previous failure was a fluke. Sadly the pattern returned. So after the hard reboot I deleted the Software Distribution and (hidden) $WinREAgent folders, let the installation rebuild, turned off the real-time anti-virus setting immediately after I got the prompt to restart the PC, clicked on Restart, and again the update worked--and I found that the monitoring had been turned back on during the update.  (Disclaimer is that for the sake of brevity I intentionally omitted something here, but it's covered in step 9 at the bottom of this message where it is more relevant.)

Obviously there might be something else in play here as if that was the ONLY issue then no one's PC would be updated. But maybe that assumption is wrong and this is more prevalent than one might think.

So I'm going to list the steps I used, but with my huge, repeat, HUGE warning--turning off your anti-virus is a choice that YOU need to make if you want to try this and I take no responsibility for any negative repercussions. Folks might jump in here and say, "DON'T DO IT!!!" and I have to emphasize that they have a point. I have to assume that if you're comfortable doing this it's because you're far from being a novice when it comes to managing Windows components--if you are not comfortable doing what I'm suggesting then either find another solution (like a clean install as I previously had done) or find someone who is knowledgeable about said components, like a trusted friend or co-worker.

Either way if you decide you want to try this remember that you're taking the chance of making your PC vulnerable. Note that I did those steps in rapid succession: I got the restart message, turned off real-time monitoring, then clicked on the restart button--all within less than 20 seconds. I don't know if my PC was still vulnerable after I clicked restart and the "Updating Windows--Don't turn off your computer" screen took over. But if you decide to take the chance (and again, I am not responsible if you decide to do this--YOU ARE), and whether it works or not, ensure real-time protection is turned back on and scan your PC immediately after booting back into Windows.

Here are the steps I used. Remember that while it worked for me your own mileage may vary. I can't guarantee this will work for you, and as I stated don't attempt this if you're not comfortable mucking around with settings.

1. Make sure you have everything backed up.
   
   
2. Go to Settings->Update and Security->Windows Security, then click on the Open Windows Security Button, which will open a new window (with the screen header Security at a glance).
   
   
3. Click on Virus and threat protection. When that screen displays click on Manage settings under the Virus and threat protection settings heading, but DO NOTHING HERE YET. Just leave it open in preparation for step 10 below.
   
   
4. Return to the Settings/Update and Security/Windows Security window from which you launched the previous Windows Security window, and on the left pane click on Windows Update.
   
   
5. Verify that you have notifications turned on when your PC needs to be restarted: Click on Advanced options and under the Update Notifications heading ensure that the button to be notified is turned ON.
   • This is crucial to the process, as if that button is turned off and you aren't notified then the PC will start before you get the chance to turn off real-time monitoring. While you could choose to turn off real-time protection at anytime before step 9 below then you're leaving your PC vulnerable for a longer period of time, and I STRONGLY RECOMMEND NOT DOING THAT.
     
     
6. Click on the arrow to return to the main Windows Update screen and click on the button to Check for updates.
   
   
7. If you see a message that updates are available click the button/link to start downloading the update.
   • If the update percentage stays at 0% for a long time you might need to delete certain folders: In my case I deleted c:\Windows\Software Distribution and c:\$WinREAgent, the latter being a hidden folder. (If you get a message that you can't delete because WU has the folder open then go to Services, stop the Windows Update service, delete the folders, restart the Windows Update service, then try starting the WU download again.)
     
     
8. After the Download message reaches 100% the Installation will be displayed in that same screen. After the Installation reaches 100% a notification will appear to restart your PC: Choose the option to restart later. 
   
   
9. Return to the Windows Security/Virus and threat protection settings window and under the Real-time protection heading turn ONLY that button OFF. In my case I left the other buttons on for my successful update. Be advised that turning off other settings besides real-time protection might result in the update not working--this is the missing step in the Disclaimer I mentioned earlier, where before the upgrade to 19536.1000 I DID turn off all the buttons, and the update failed--but when I repeated these steps and turned off ONLY real-time protection--which I had originally done for 19041.1--the update succeeded.
   
   
10. Return to the Settings/Windows Update window and there should be a message stating that a restart is needed. Click on that to restart.
    

I went over these steps and believe I have not left anything out. I won't repeat the warnings, so if you decide to do this and something goes wrong then don't send me any nastygrams. But I would like to see feedback if you were confident enough in your technical knowledge to try this, and whether it worked for you or not.

Good luck, and thanks.

Mike (profile name Creetisvan)