Windows Upgrade Help and more

Can confirm. You could also try running the Windows Update troubleshooter first, as it can sometimes clear up these types of errors.

I'm trying to upgrade my Windows 10 PC to Windows 11, but the setup keeps failing with error code 0xC1900101. My main worry is my files. The upgrade assistant says everything is compatible, but I've heard horror stories. Does this process automatically create a full system backup I can restore, or do I need to manually back up everything to an external drive first? I don't want to lose years of photos and documents.

That error usually means a driver or software conflict. The upgrade doesn't automatically create a full backup you can restore, so you should manually back up your important files to an external drive first. Once your photos and docs are safe, try running the Windows Update Troubleshooter and temporarily unplug any non-essential peripherals before attempting the upgrade again. Let me know if that works.

You could also try using the Media Creation Tool to perform a clean install instead, which sometimes bypasses upgrade errors.

Another option is to manually create a system image backup using Windows' built-in Backup and Restore tool before trying again, just to be safe.

Yeah, I had the same problem with that exact error. It turned out a piece of old security software was blocking it, even though the assistant said I was good. Good luck!

Agreed. I had the same problem. For me, the error was fixed by temporarily disconnecting all my non-essential USB devices before starting the upgrade.

Same here. Just to be sure, have you tried running the setup after a clean boot to rule out any software conflicts?

Also, could you check if you have enough free space on your system drive, as that's a common culprit for that error?