Microsoft's August Update Causes Errors on Windows Server 2016 Systems
Microsoft has acknowledged that the August 2026 security update may trigger 0xc0000409 errors on Windows Server 2016 systems where the Compatibility Appraiser diagnostic service is enabled.
The issue causes the CompatTelRunner.exe (Compatibility Appraiser Telemetry Runner) process to crash, resulting in recurring Application Error events with Event ID 1000 and exception code 0xc0000409. Although these failures do not affect device functionality, users may see associated event log warnings.
Microsoft states that this known issue affects both physical devices and virtual machines, including VMware and Azure environments.
The company is working on a fix that will ship with a future Windows update, but no timeline has been shared for a permanent solution.