Windows App Certification Kit - Test Results :[HRESULT 0x8007007F] An error occurred during TAEF startup. (Failed to load the custom test mode DLL at "......\TAEF\TE.TestMode.Container.dll

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Windows App Certification Kit - Test Results :[HRESULT 0x8007007F] An error occurred during TAEF startup. (Failed to load the custom test mode DLL at "......\TAEF\TE.TestMode.Container.dll

Divyns Lin 41

Hi MSFT,

I created a UWP package and ran the App Certification. Last month there were no issues, but recently an error started to appear. I’m not sure if this is caused by a Windows update or another change.

I reinstalled SDK 22621, but the error still occurs.

Do you have any suggestions or tips?

Thank you.

Error Found: The app launch test detected the following errors:
- [HRESULT 0x8007007F] An error occurred during TAEF startup. (Failed to load the custom test mode DLL at "C:\Program Files (x86)\Windows Kits\10\Testing\Runtimes\TAEF\TE.TestMode.Container.dll".)

Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-11-28T07:46:52.44+00:00

Hi @Divyns Lin , do you have any update on Danny's reponse?

3 answers

Your answer

Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-11-28T07:46:52.44+00:00

Hi @Divyns Lin , do you have any update on Danny's reponse?

Answer 1

Danny Nguyen (WICLOUD CORPORATION) 5,410 Microsoft External Staff Moderator

Hi,

Could you please run a quick harness check so we can confirm whether the issue is with the test mode plugin or something broader?

Verify presence & signature of the plugin Path: C:\Program Files (x86)\Windows Kits\10\Testing\Runtimes\TAEF\TE.TestMode.Container.dll
- Right‑click → Properties → Digital Signatures tab. Confirm it shows a valid Microsoft signature.
- In Details tab note the File version (for SDK 10.0.22621 it should start with 10.0.22621.).
- If the file is missing, let me know immediately.

Run TAEF core directly (just to prove the engine itself loads):

   
   cd "C:\Program Files (x86)\Windows Kits\10\Testing\Runtimes\TAEF"
   
   te.exe /list

Please post back with:
- Present / missing DLL?
- Signature valid?
- File version string?
- Exact output from te.exe /list (copy/paste).

If the DLL is present but signed and we still get the WACK failure, next step is a dependency/export check. If the DLL is corrupt or missing, we’ll do a clean SDK reinstall . Archive the entire TAEF directory for reference before a full SDK uninstall if needed.

Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-10-28T03:27:53.3766667+00:00

Hi there — just checking in as I haven’t heard back on this thread for a while. Did the steps provided help you resolve the App Certification Kit test result issue?

If it worked out, please consider marking the answer as accepted so others can benefit from it too. If you’re still running into problems or need clarification on any of the HRESULT codes, I’m happy to assist further!
Divyns Lin 41 Reputation points

2025-10-28T05:07:08.88+00:00

hi Danny

Thanks for your reply.

1 I checked the TE version — the file exists, but the version is not as expected.

2 run TAE core
Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-10-28T07:50:09.5466667+00:00

This might indicate that this is because of version mismatch. I suggest archiving the TAEF folder and doing a clean reinstall of the Windows SDK.

After that try verifying the version again like above and see if it works.
Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-11-11T10:45:21.9366667+00:00

Hi, just checking in again, has there been any development on this problem?
Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-11-17T02:45:31.3766667+00:00

Just checking in — I haven’t heard back from you for a while,

I hope everything works out as you expected. I understand things can get busy or priorities may shift. If you’re still experiencing the issue or need further support, feel free to jump back in at any time — I will always be here and happy to help. If the solution works out for you, please consider marking this answer as accepted.

Wishing you all the best with your work!

Answer 2

RWZ 0

I have same error

[HRESULT 0x8007007F] An error occurred during TAEF startup. (Failed to load the custom test mode DLL at "C:\Program Files (x86)\Windows Kits\10\Testing\Runtimes\TAEF\TE.TestMode.Container.dll".) User's image

Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-12-03T02:56:56.2133333+00:00

Have you tried doing a clean reinstall of the Windows SDK?
RWZ 0 Reputation points

2025-12-03T15:23:59.1133333+00:00

i have try reinstall windows 11 SDK / update vs code 2026

download new sdk
https://developer.microsoft.com/zh-cn/windows/downloads/windows-sdk/
but the error still occurs.

Answer 3

RWZ 0

try

rename
TE.TestMode.Container.dll
to
TE.TestMode.Container.bad.dll

it may be work .

I angrily deleted this file. It's amazing . it works so well now.

Danny Nguyen (WICLOUD CORPORATION) 5,410 Reputation points Microsoft External Staff Moderator

2025-12-04T02:35:33.2333333+00:00

That's great.

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Windows App Certification Kit - Test Results :[HRESULT 0x8007007F] An error occurred during TAEF startup. (Failed to load the custom test mode DLL at "......\TAEF\TE.TestMode.Container.dll

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