Upgrading Windows 11 has long been a secure and seamless affair. More often than not, it goes through without making any fuss at all, ensuring your PC is able to get the latest gears and features to not only enhance performance but also take on threats head-on.
However, sometimes the process can fail with the error code 0xC1900101 – 0x40021, taking the center stage on your PC. In this hands-on guide, I’m going to discuss the 7 most effective ways to fix the 0xC1900101 – 0x40021 Windows 11 error. If this issue has stalled the software upgrade on your Windows device as well, now is the right time to fix it for good. Keep reading to…
Fix 0xC1900101 – 0x40021 Windows 11 Upgrade Error
What causes the 0xC1900101 – 0x40021 error to crop up? Well, it usually indicates a driver-related problem or an interruption during the installation’s second boot phase. It shows up due to multiple reasons, such as outdated drivers, conflicting software, insufficient storage, or issues with system files that prevent Windows from completing the upgrade.
1. Update All Device Drivers
Note that outdated or incompatible drivers—especially chipset, graphics, storage, and network drivers— can get in the way of the Windows upgrade process and trigger the error. Therefore, make sure to update all device drivers on your PC.
- To get going, launch the Device Manager from the Start menu.
- After that, check for yellow warning icons beside devices such as Display Adapters, Storage Controllers, or Network Adapters.
- Then, right-click each device > choose Update driver and restart your PC, and retry the upgrade.
2. Uninstall Third-Party Antivirus Software
It’s worth pointing out that security programs can block system-level changes required during the Windows installation, making the upgrade to fail.
- On your Windows device, dive into the Settings app > Apps > Installed Apps.
- Now, select your third-party antivirus application and click Uninstall.
- After that, you have to restart your PC and retry the Windows 11 upgrade, and reinstall the antivirus afterward if needed
3. Disconnect External Devices
Keep an eye on the USB drives, external HDDs, docks, Bluetooth dongles, or peripherals as they are also equally responsible for interrupting the second boot phase of installation, leading to the 0xC1900101 – 0x40021 error.
- Therefore, make sure to remove all external devices except your mouse and keyboard.
- Next, you have to unplug USB hubs or adapters.
- Next up, restart your computer and attempt the Windows 11 upgrade again.
4. Ensure Enough Storage Space for the Upgrade
It’s also important to note that Windows needs temporary space for unpacking upgrade files. Bear in mind that cluttered disk space can cause installation failures mid-process.
- Navigate to Settings > System > Storage.
- After that, be sure to delete temporary files, large unused items, or old installers.
- Up next, empty the Recycle Bin and free up at least 20–25 GB of free space before running the upgrade.
5. Run SFC and DISM to Repair System Files
Always remember the fact that corrupted or missing system files also tend to prevent Windows from completing the installation safely, resulting in this error code.
- Fire up Windows Terminal (Admin) and run sfc /scannow and wait for the scan to finish.
- After that, run the following commands one by one:
- DISM /Online /Cleanup-Image /CheckHealth
- DISM /Online /Cleanup-Image /ScanHealth
- DISM /Online /Cleanup-Image /RestoreHealth
- Restart your PC and try upgrading again
6. Disable Fast Startup in Windows
Do you know that Fast Startup stores kernel data between restarts, which may interfere with reboot-based upgrade phases? Thus, I’d recommend you disable it in order to have a clean boot environment.
- On your PC, head over to Control Panel > Power Options > Choose “Change what the power buttons do“.
- Click Change settings that are currently unavailable.
- Uncheck Turn on fast startup and save changes and reboot your system.
7. Perform the Upgrade Using the Windows 11 Installation Assistant
No luck as yet? If the problem continues to halt the software update on your PC, perform the upgrade with the help of Windows 11 Installation Assistant. For those unfamiliar, the Installation Assistant bypasses many background processes and provides a more stable upgrade path compared to Windows Update, reducing the chance of upgrade errors.
- To begin, you have to download the Windows 11 Installation Assistant from Microsoft’s official website.
- Run the tool and follow the on-screen steps to begin the upgrade.
- Then, make sure to wait for the process to complete and restart your PC when prompted.
Wrapping up..!
There you go! The 0xC1900101 – 0x40021 Windows 11 upgrade error typically results from driver conflicts, insufficient storage, faulty peripherals, or system file corruption. By applying the methods above, you eliminate the most common causes and create a stable environment for the upgrade to complete successfully.
Keeping your drivers updated, disconnecting unnecessary devices, maintaining adequate storage, and using built-in repair tools all contribute to preventing this error in the future. After following these solutions, your Windows 11 installation should proceed smoothly, allowing you to enjoy the latest features and enhancements without interruption.
