Windows 10 ESU Licensing Preparation Package (KB5126256) is installed

KB5126256 alone does not start ESU. It only prepares Windows 10 version 22H2 for ESU licensing and enrollment. The device must still be enrolled in the ESU program to receive security updates.

For this scenario, check these items in order:

1. Confirm the device is on Windows 10, version 22H2.
2. Confirm a security update released on or after October 14, 2025 is already installed. KB5126256 must be installed after that update.
3. Restart the device. The preparation package requires a restart.
4. Try the enrollment again later. A similar Windows 10 ESU enrollment issue has been reported where enrollment can keep spinning or fail temporarily even when prerequisites are met.
5. If ESU key activation is being used, verify the key is installed and activated:
   • Open an elevated Command Prompt.
   • Run slmgr /dlv all
   • Verify the ESU key shows as licensed.
6. If updates still do not install, install and activate the ESU key again using an elevated Command Prompt:
   • slmgr /ipk <ESU key>
   • slmgr /ato <Activation ID>
7. If installation or activation fails with prerequisite-related errors:
   • If the update says not applicable, verify the package matches the OS edition and architecture, then restart and try again.
   • If activation returns 0xC004F050, verify all ESU prerequisite updates are installed successfully, confirm the correct key is being used, then restart and try again.

If the problem continues after the restart and prerequisite checks, collect C:\Windows\Logs\CBS\CBS.log and contact Microsoft Support.

References:

• Extended Security Updates (ESU) Licensing Preparation Package for Windows 10 | Microsoft Support
• Troubleshoot issues in ESU
• Issue with ESU for Windows 10 - Microsoft Q&A
• esu for windows 10 fails - Microsoft Q&A