[BUG] CoworkVMService fails to start with ExitCode 1066 — Windows 11 Pro 24H2 Build 26100

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

CoworkVMService fails to start with ExitCode 1066 on Windows 11 Pro 24H2 (Build 26100). The Cowork UI shows "Failed to start Claude's workspace — VM service not running. The service failed to start." The error persists after rebooting, reinstalling the workspace, deleting and re-downloading the VM bundle, manually recreating the HNS network and NetNat rule, enabling the HNS PowerShell module, and verifying all Hyper-V services are running. The service dependency (staterepository) is confirmed running. The Hyper-V Host Compute Service is operational. The cowork-svc.exe binary exists at the correct path. The service simply fails to start with no actionable error message in Event Viewer — all CoworkVMService log entries show empty messages due to missing event description DLLs in the MSIX package

Windows 11 Pro, 24H2, Build 26100
Claude Desktop v1.1.6679
ExitCode 1066 from CoworkVMService
All the troubleshooting steps you've already tried (HNS network, NetNat, vm_bundles deletion, etc.)

What Should Happen?

Cowork should successfully start the VM service and load the workspace without errors. The CoworkVMService should start automatically, initialize the VM, and allow tasks to be executed normally.

Error Messages/Logs

Failed to start Claude's workspace — VM service not running. The service failed to start.

CoworkVMService ExitCode: 1066

sc.exe qc CoworkVMService:
SERVICE_NAME: CoworkVMService
        TYPE               : 210  WIN32_PACKAGED_PROCESS
        START_TYPE         : 2   AUTO_START
        ERROR_CONTROL      : 0   IGNORE
        BINARY_PATH_NAME   : "C:\Program Files\WindowsApps\Claude_1.1.6679.0_x64__pzs8sxrjxfjjc\app\resources\cowork-svc.exe"
        DEPENDENCIES       : staterepository
        SERVICE_START_NAME : LocalSystem

Get-WinEvent (Microsoft-Windows-Hyper-V-Compute-Operational):
- The Host Compute Service is starting. (10:17:29 AM)
- The Host Compute Service is starting. (10:07:28 AM)

Event Viewer (Application log):
- All CoworkVMService entries show: "The description for Event ID '1' in Source 
'CoworkVMService' cannot be found. The local computer may not have the necessary 
registry information or message DLL files to display the message."

Start-Service error:
Start-Service : Failed to start service 'Claude (CoworkVMService)'.

HNS Network: cowork-vm-nat (NAT, 172.16.0.0/24) — present and active
NetNat: cowork-vm-nat (172.16.0.0/24) — present and active
staterepository service: Running
Hyper-V: Enabled


Windows 11 Pro, 24H2, Build 26100
Claude Desktop v1.1.6679
ExitCode 1066 from CoworkVMService
All the troubleshooting steps you've already tried (HNS network, NetNat, vm_bundles deletion, etc.)

Steps to Reproduce

1. Install Claude Desktop (v1.1.6679) on Windows 11 Pro 24H2 (Build 26100)
2. Open Claude Desktop and navigate to the Cowork tab
3. Observe error: "Failed to start Claude's workspace — VM service not running"
4. Attempted fixes (all failed):
   - Restarted Claude Desktop
   - Rebooted computer
   - Deleted vm_bundles folder at %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\vm_bundles and relaunched to force fresh download
   - Enabled Hyper-V via PowerShell
   - Manually removed and recreated HNS network (cowork-vm-nat, 172.16.0.0/24)
   - Manually removed and recreated NetNat rule (cowork-vm-nat, 172.16.0.0/24)
   - Confirmed staterepository dependency service is running
   - Confirmed Hyper-V Host Compute Service is running
   - Attempted Start-Service -Name CoworkVMService manually — fails with ExitCode 1066
5. Error persists unchanged after all of the above

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

Never worked — Cowork has not successfully started on this system since initial installation.

Claude Code Version

Claude Desktop v1.1.6679

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Subscription: Pro

All diagnostic commands run as Administrator in PowerShell.

Related GitHub issues with similar symptoms:
- #27801 — CoworkVMService fails to start, Windows regression
- #27010 — Cowork VM service not running on Windows 10 Pro
- #25206 — VM starts but crashes within 5 minutes, service unrecoverable
- #25419 — sandbox-helper fails, VM service won't start (Win 11 Pro)

This issue appears related to the broader CoworkVMService regression 
affecting multiple Windows users since approximately Claude Desktop v1.1.3189.