[Bug]: Windows Sandbox failed to initialize

[wangyk55]

Windows Sandbox version

0.5.3.0

Windows build number

10.0.26200.0

Other software

No response

Steps to reproduce the bug

1. Install Windows Sandbox from Windows Features in Control Panel.
2. Start Windows Sandbox.
3. A window about downloading and updating pops up.
4. An error window pops up, saying "Windows Sandbox failed to initialize. Exception of type 'System.Exception' was thrown." with no error code.

Expected result

Windows Sandbox is supposed to start.

Actual result

The "downloading and updating" window only pops up at the first time after installing Windows Sandbox. Then each time I start Windows Sandbox, the error window pops up immediately.

Included System Information

Edition Windows 11 Pro
Version 25H2
Installed on ‎7/‎18/‎2025
OS build 26200.8457
Experience Windows Feature Experience Pack 1000.26100.304.0

[UBarney]

I am seeing the same issue on Windows 11 Pro, build 10.0.26200.

This is very frustrating because Windows Sandbox is one of the Pro features I paid for and expected to be supported. Right now I cannot use a documented Windows Pro feature at all, even after trying the usual recovery steps.

What I have tried:

• Reinstalled Windows Sandbox
• Cleared/recreated C:\ProgramData\Microsoft\Windows\Containers
• Tested with networking disabled via .wsb
• Tested with both networking and vGPU disabled via .wsb
• Ran DISM /Online /Cleanup-Image /RestoreHealth
• Ran sfc /scannow
• Reset the transactional resource manager with fsutil resource setautoreset true C:\
• Confirmed Hyper-V services are running

The VM appears to be created and booted, but Windows Sandbox still fails to initialize. Relevant logs include:

• Microsoft-Windows-Hyper-V-Compute-Operational: notification 3 / 0xC0370106
• Microsoft-Windows-Hyper-V-Worker-Admin: guest OS successfully booted
• Windows Error Reporting / CBS servicing failures involving 0x80071a90

At this point this does not look like a user configuration problem. It looks like a regression or servicing/component issue in the Windows Sandbox stack for build 26200.

As a paying Windows 11 Pro customer, I feel misled when a documented Pro feature is broken like this with no clear workaround. Could Microsoft please acknowledge whether this is a known issue and provide a fix or mitigation?