0xc1900101
A Windows upgrade (for example to a new Windows 11 version) failed and rolled back. It is almost always a driver problem.
How to fix it
- Unplug everything you do not need: USB drives, docks, printers, extra monitors, card readers.
- Update graphics, storage, network and chipset drivers from the PC maker's website.
- Uninstall third-party antivirus before upgrading (you can reinstall it afterwards).
- Make sure there is at least 20 GB free on C:.
- Try the upgrade from the Windows Installation Assistant or a USB stick made with the Media Creation Tool.
Is it serious?
Fixable in most cases. The extra code after the dash (0x20017, 0x40017) tells a technician which phase failed.