Windows ChatGPT Desktop - Codex fails to start ("The parameter is incorrect") and ChatGPT hangs (Application Hang 1002)

What version of the Codex App are you using (From “About Codex” dialog)?

Latest version bundled with ChatGPT Desktop

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Windows 11 Home 25H2 (Build 26200.8875) x64

What issue are you seeing?

I am experiencing this issue on the latest ChatGPT Desktop running on Windows 11 Home.

When I launch Codex from the ChatGPT Desktop application, the Windows UAC prompt appears normally. After approving administrator permission, codex-windows-sandbox-setup.exe immediately exits, Windows displays "The parameter is incorrect.", and ChatGPT Desktop becomes unresponsive.

Environment:

• ChatGPT Plus
• Windows 11 Home 25H2
• OS Build: 26200.8875
• Latest ChatGPT Desktop

Symptoms:

• Clicking Codex triggers the Windows UAC prompt.
• After approving administrator permission, codex-windows-sandbox-setup.exe immediately exits.
• Windows displays:

"The parameter is incorrect."

• ChatGPT Desktop freezes.
• Windows Event Viewer records:

Application Hang (Event ID 1002).

• No log files are generated under %LOCALAPPDATA%\OpenAI\Codex.

Troubleshooting already performed:

• Reinstalled ChatGPT Desktop.
• Restarted Windows multiple times.
• Verified Virtual Machine Platform is enabled.
• Verified Windows Hypervisor Platform is enabled.
• Confirmed codex.exe and codex-windows-sandbox-setup.exe exist.
• Manually launched the helper executable.
• No log files are created.

This issue completely prevents me from using Codex.

If additional diagnostic information is helpful, I would be happy to provide it.

If this is not the same root cause, please let me know and I will gladly open a separate issue with additional diagnostic information.

Thank you for your time and for reviewing this report.

What steps can reproduce the bug?

1. Launch ChatGPT Desktop.
2. Click Codex.
3. Windows displays the UAC prompt.
4. Approve administrator permission.
5. codex-windows-sandbox-setup.exe starts.
6. Windows immediately displays "The parameter is incorrect."
7. ChatGPT Desktop hangs.

What is the expected behavior?

Codex should start successfully and open a working coding session.

Additional information

This issue was investigated through an extensive troubleshooting session.

Verified facts:

• Installation completed successfully.
• Codex binaries exist.
• The helper executable (codex-windows-sandbox-setup.exe) starts and exits immediately.
• No Codex log files (*.log) are generated.
• ChatGPT Desktop freezes.
• Windows Event Viewer reports Application Hang (Event ID 1002).

Business impact:

I subscribed to ChatGPT Plus primarily because Codex was a key feature that I intended to use together with Higgsfield MCP for my production workflow.

Unfortunately, I have never been able to launch Codex successfully, even once.

Because of this issue, I have been completely unable to use the feature that influenced my decision to subscribe.

I have spent many hours troubleshooting this issue, including reinstalling the application, verifying Windows virtualization features, checking Event Viewer logs, confirming the Codex installation files, and working through multiple troubleshooting steps.

This issue has completely blocked my intended workflow.

I would appreciate it if the engineering team could investigate and resolve this issue.

I will contact OpenAI Support separately regarding my subscription and customer support request.

If needed, I can provide:

• Windows error screenshots
• Event Viewer screenshots
• Codex installation screenshots
• Additional diagnostic information