How to fix
Windows installation error 0xC1900101 – 0x40021
on Windows

Hi, so I tried upgrading from Windows version 22H2 to 23H2 but it failed with an error 0xC1900101 - 0x40021 "The installation failed in the SECOND_BOOT phase with an error during SYSPREP_RESPECIALIZE operation."

Windows updates and upgrades are essential to maintain the operating system due to the latest features, security patches, and myriad other improvements. Unfortunately for some users, this process might fail with an error code 0xC1900101 - 0x40021, which stops the upgrade process and reverts the system to the earlier version. This can happen whenever one wants to upgrade to the latest Windows 11 or move from Windows 22H2 to Windows 23H2, for instance.

It is evident that the reasons for the 0xC1900101 - 0x40021 could vary greatly - from corrupted system files, conflicting third-party software, incompatible hardware or drivers, and similar. To address this, you should first make sure that your PC meets system requirements for the new Windows version you're attempting to install - using a free tool from Microsoft can be useful here.

Additionally, there are several troubleshooting steps you could perform in order to fix the 0xC1900101 - 0x40021 error. You can start this process with the built-in troubleshooter which can identify problems automatically in most cases. Next, check for corrupted system files by running special commands in the elevated Command Prompt.

The 0xC1900101 - 0x40021 error might be caused by third-party software (often anti-malware software) in many cases, so running a clean boot might resolve the problem. Clean boot disables non-essential startup programs and services that could be interfering with the upgrade process.

For a more automated solution, consider using a reliable PC repair tool like [d1], which can automatically diagnose and repair underlying Windows issues, potentially resolving the 0xC1900101 - 0x40021 error and other related problems. It offers a convenient and efficient way to address various Windows issues, ensuring an overall smoother PC operation.

Fix 1. Employ the Windows Health Check app

Windows Health Check app is a built-in tool that assesses your system's compatibility with the new Windows version. It scans your hardware and identifies any potential issues that could lead to the 0xC1900101 - 0x40021 error. If it detects problems, it provides recommendations to address them.

• Open your browser and download the PC Health Check app from the official Microsoft website.
• After it's downloaded, click the prompt within your browser to start the installation process.
• Agree to the terms and click Install.
• In a few seconds, the app should be installed - click Finish.
• Under Introducing Windows 11, click Check now.
• You will be provided with one of the following results:
  This PC meets Windows 11 requirements
  This PC doesn't currently meet Windows 11 system requirements
  Your organization manages updates on this PC
• If your PC meets the requirements, proceed with the solutions below. If that's not the case, it might sometimes be possible to upgrade even if the hardware is not supported.

Fix 2. Run Windows update troubleshooter

Windows update troubleshooter is a diagnostic tool designed to identify and resolve problems with Windows updates. 

• Type Troubleshoot into the Windows search bar and press Enter.
• Next, on the right side of the window, select Additional troubleshooters/Other troubleshooters.
• Scroll down to locate the Windows update option and click on it.
• Click on Run the troubleshooter/Run and allow the troubleshooter to finish.
• Restart your computer and try updating Windows again.

Fix 3. Reset Windows update components

This solution resolves issues related to update downloads and installations - it can help eliminate potential causes of the 0xC1900101 - 0x40021 error.

• Type cmd in Widnows search bar.
• Right-click on Command Prompt and select Run as administrator.
• When the User Account Control window shows up, click Yes.
• Copy and paste in the following commands, pressing Enter each time:
  net stop wuauserv
  net stop cryptSvc
  net stop bits
  net stop msiserver
  ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
  ren C:\Windows\System32\catroot2 Catroot2.old
  net start wuauserv
  net start cryptSvc
  net start bits
  net start msiserver
• Close down the Command Prompt and see if the problem is resolved.

Fix 4. Perform Clean Boot

Clean Boot disables non-essential startup programs and services, helping to eliminate potential conflicts that might cause the upgrade error.

• Press Win + R, type msconfig, then press Enter.
• Select the Services tab and tick the Hide all Microsoft services checkbox.
• Pick Disable all.
• Go to the Startup tab and click Open Task Manager.
• Here, right-click on each of the non-Windows entries and select Disable.
• Close down the Task Manager.
• Go to the Boot tab and tick the Safe boot option
• Restart your system.

Fix 5. Run SFC, DISM, and CHKDSK

Running certain commands in an elevated Command Prompt can ensure that system files, image files, and disk are in good condition.

• Open Command Prompt as administrator.
• In the Command Prompt window, paste the following command and hit Enter:
  sfc /scannow
• Next, use the following commands, pressing Enter each time:
  Dism /Online /Cleanup-Image /CheckHealth
  Dism /Online /Cleanup-Image /ScanHealth
  Dism /Online /Cleanup-Image /RestoreHealth
  (Note: if you get an error executing this last command, add /Source:C:\RepairSource\Windows /LimitAccess to it and try again).
• Finally, use the following command:
• chkdsk c: /f
  (Note: use chkdsk c: /f /r /x command if you are using SSD as your primary partition)
• If you receive an error, type in Y, close down Command Prompt and restart your system.
• Wait until the scan is finished - you can find the results in the Event Viewer.
• Restart your device.

Fix 6. Use Media Creation Tool/ISO

Using the Media Creation Tool or an ISO file to upgrade Windows can sometimes resolve the error by providing a more stable and reliable installation method. Before proceeding, make sure third-party security software is uninstalled and all the external devices, such as USB sticks, are disconnected.

• Visit the official Microsoft website and download Windows 10 installation media. [Windows 11 version]
• Double-click the installer and select Yes when UAC shows up.
• Agree to the terms and click Next.
• Select Upgrade this PC now and click Next.
• Wait till Windows downloads all the necessary files.
• Restart your device when finished.