[BUG] Cowork fails with Plan9 share 'z' Access Denied (0x80070005) — Windows 11 Pro, persists after all known workarounds

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?

[BUG] Cowork fails with Plan9 share 'z' Access Denied (0x80070005) — Windows 11 Pro, persists after all known workarounds

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop

Environment

| Property | Value |
|---|---|
| OS | Windows 11 Pro |
| Claude Desktop version | 1.569.0.0 |
| Subscription | Pro/Max |
| Hyper-V | Enabled, vmms and vmcompute both Running |
| VPN | None |

What's Wrong?

Cowork workspace fails to start with a Plan9 file share access denied error. The error persists after rebooting, reinstalling the workspace, and applying all known community workarounds.

Error Message

Failed to start Claude's workspace
failed to add Plan9 share 'z': HcsWaitForOperationResult failed with HRESULT 0x80070005: {"Error":-2147024891,"ErrorMessage":""}
Restarting Claude or your computer sometimes resolves this. If it persists, you can reinstall the workspace.

Steps to Reproduce

1. Open Claude Desktop (version 1.569.0.0) on Windows 11 Pro
2. Click on Cowork tab
3. Error appears: "Failed to start Claude's workspace — failed to add Plan9 share 'z'"
4. Restart Claude Desktop — same error
5. Reboot computer — same error
6. Apply all workarounds listed below — same error

Expected Behavior

Cowork should start the VM workspace successfully and mount the Plan9 share without access denied errors.

Actual Behavior

The VM bundle downloads and prepares correctly. The service starts, attempts to configure the Windows VM service, and fails at the Plan9 share mounting step with HRESULT 0x80070005 (Access Denied).

Log Output

From %APPDATA%\Claude\logs\cowork_vm_node.log:

2026-04-04 19:26:06 [info] [VM] Loading vmClient (TypeScript) module...
2026-04-04 19:26:06 [info] [VM] Module loaded successfully
2026-04-04 19:26:13 [info] [KernelBugMonitor] State reset
2026-04-04 19:26:13 [info] [VM:start] Beginning startup, bundlePath=C:\Users\Doron\AppData\Roaming\Claude\vm_bundles\claudevm.bundle
2026-04-04 19:26:13 [info] [VM:start] Bundle version: 5680b11bcdab215cccf07e0c0bd1bd9213b0c25d
2026-04-04 19:26:13 [info] [VM:start] VM instance ID: fa355113-34f8-4e2f-9105-726709c49d76
2026-04-04 19:26:13 [info] [VM:steps] download_and_sdk_prepare started
2026-04-04 19:26:13 [info] [VM:steps] download_and_sdk_prepare completed (6ms)
2026-04-04 19:26:13 [info] [VM:steps] load_swift_api started
2026-04-04 19:26:13 [info] [VM:steps] load_swift_api completed (0ms)
2026-04-04 19:26:13 [info] [Callbacks] Initializing VM event callbacks...
2026-04-04 19:26:13 [info] [Callbacks] VM event callbacks initialized
2026-04-04 19:26:13 [info] [VM:start] Copying smol-bin.x64.vhdx to bundle
2026-04-04 19:26:13 [info] [VM:start] smol-bin.x64.vhdx copied successfully
2026-04-04 19:26:13 [info] [VM:start] Configuring Windows VM service...
2026-04-04 19:26:18 [error] [VM:start] Startup failed: Error: VM service not running. The service failed to start.
2026-04-04 19:26:18 [info] [VM:start] Skipping auto-reinstall (already attempted once)

Windows Event Log (System):

The Claude service terminated unexpectedly. It has done this 1 time(s).

Issues Found During Troubleshooting

1. Missing sessiondata.vhdx

The sessiondata.vhdx file was not created during Cowork's bootstrap process. It was not visible in the bundle directory listing. Had to be created manually:

New-VHD -Path "$env:APPDATA\Claude\vm_bundles\claudevm.bundle\sessiondata.vhdx" -Dynamic -SizeBytes 10GB

After creating it, the error changed from "VM service not running" to the Plan9 share access denied error - meaning we got further but hit the next problem.

2. Hyper-V Administrators group was empty

The user account was not in the Hyper-V Administrators group. The group had zero members:

PS> net localgroup "Hyper-V Administrators"
Members
-------------------------------------------------------------------------------
(empty)

Fixed with:

net localgroup "Hyper-V Administrators" Doron /add

Did not resolve the Plan9 error.

3. SYSTEM ACL on vm_bundles

Applied SYSTEM full control per issue #38188:

icacls "$env:APPDATA\Claude\vm_bundles" /grant "SYSTEM:F" /T

Successfully processed all 17 files. Did not resolve the Plan9 error.

4. SYSTEM ACL on user profile root

icacls "C:\Users\Doron" /grant "SYSTEM:F"

Did not resolve the Plan9 error.

Workarounds Attempted (all failed)

| Workaround | Result |
|---|---|
| Reboot computer (multiple times) | Same error |
| Delete vm_bundles and let re-download | Same error |
| Manually create sessiondata.vhdx | Changed error from "VM service not running" to Plan9 access denied |
| Add user to Hyper-V Administrators group + reboot | Same Plan9 error |
| Grant SYSTEM:F on vm_bundles /T | Same Plan9 error |
| Grant SYSTEM:F on C:\Users\Doron | Same Plan9 error |
| Confirm vmcompute service running | Was running, not the issue |
| Check for stale HNS network | Only "Default Switch" present, no stale cowork network |
| Check for stuck VM via hcsdiag list | No stuck VMs found |

Additional Notes

• No cowork-service.log file exists at %APPDATA%\Claude\logs\ — only cowork_vm_node.log is present
• The service binary path is confirmed correct: C:\Program Files\WindowsApps\Claude_1.569.0.0_x64__pzs8sxrjxfjjc\app\resources\cowork-svc.exe
• Running cowork-svc.exe directly returns "Access is denied" (expected for MSIX packaged service)
• No VPN, no antivirus interference detected
• Regular Claude Chat mode works without issues — only Cowork is affected

Related Issues

• #38188 — HCS 0x80070005 resolved by granting SYSTEM permissions (partial fix, didn't resolve Plan9 share)
• #43441 — Access Denied on sessiondata.vhdx
• #25419 — sandbox-helper fails to mount host share
• #31877 — Duplicate Plan9 shares causing HCS failure
• #27801 — VM service not running, persists after reboot

What Should Happen?

It should implement the CoWork feature for me.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Desktop (version 1.569.0.0) on Windows 11 Pro
2. Click on Cowork tab
3. Error appears: "Failed to start Claude's workspace — failed to add Plan9 share 'z': HcsWaitForOperationResult failed with HRESULT 0x80070005"
4. Restart Claude Desktop — same error
5. Reboot computer — same error
6. Reinstall workspace — same error

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

CoWortk Never worked for me

Claude Code Version

1.569.0.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_