Forum Discussion
Configuration Manager manifest synchronization failing since 8 July 2026
Has anyone else experienced Configuration Manager Updates and Servicing synchronization failures since 8 July 2026?
We have three independent Microsoft Configuration Manager hierarchies:
Test environment
Production T0 environment
Production T1 environment
All three started showing the same SMS_DMP_DOWNLOADER error during the last three days.
The affected request is sent to:
https://sccm.manage.microsoft.com/SCCMConnectedService.svc/Manifest
Configuration Manager builds a hierarchy-specific request containing the Tenant, Version, Ring, and Branch parameters. However, the endpoint now returns only:
OK
The resulting file is:
ConfigMgr.Update.Manifest.cab Size: 2 bytes Hex: 4F 4B Content: OK
Because this is not a valid signed CAB file, dmpdownloader.log records:
manifest.cab (http response) size is 2 Error in verifying the trust of file ConfigMgr.Update.Manifest.cab' WARNING: Failed to call IsFileTrusted WARNING: Failed to download and verify the manifest.cab. We cant get info in Updates and Servicing mode.
2 Replies
Hi Rajha,
The fact that this started almost simultaneously across three independent ConfigMgr hierarchies strongly suggests this is not a local Configuration Manager issue, but rather a Microsoft service-side or endpoint problem.
Receiving a plain "OK" response instead of a signed ConfigMgr.Update.Manifest.cab explains why SMS_DMP_DOWNLOADER fails the trust validation. It has nothing valid to verify.
I'd recommend:
- Capturing the HTTP response headers and body (using Fiddler or another network trace) to confirm the endpoint is consistently returning only OK.
- Checking whether any proxy, SSL inspection, or firewall device could be modifying the response, although this is unlikely if all three environments are affected.
- Reviewing the Microsoft 365 Admin Center and the Configuration Manager release notes for any recent service advisories.
- Opening a Microsoft support case and providing the dmpdownloader.log, ConfigMgr version, tenant ID, and the raw HTTP response. The fact that multiple independent hierarchies exhibit the same behavior is a strong indicator that Microsoft can use to expedite the investigation.
Please post an update if you hear back from Microsoft. It would be helpful for others seeing the same manifest synchronization failure.
Hi rajha1750, because this started at the same time across three independent hierarchies, I would suspect a Microsoft service-side issue or endpoint response change rather than a local hierarchy problem. Keep the small two-byte response file, SMS_DMP_DOWNLOADER logs, timestamp, tenant ID, ConfigMgr version, and the exact endpoint response. I would open a Microsoft support case and mention that multiple unrelated environments are receiving only OK instead of a valid manifest CAB.
