● Covered by 1 source · 1 reportMedium impact1 neutral
August 2026 Windows Server 2016 Update Causes 0xc0000409 Errors
Key points
- August 2026 update causes 0xc0000409 errors on Windows Server 2016.
- CompatTelRunner.exe crashes when Compatibility Appraiser is enabled.
- Affects physical and virtual machines, including VMware and Azure.
- Microsoft states device functionality is not impacted; a fix is coming.
August Update Triggers Application Errors
Microsoft has confirmed that the August 2026 security update for Windows Server 2016 can lead to 0xc0000409 errors. These errors occur on systems where the Compatibility Appraiser diagnostic service is active, causing the CompatTelRunner.exe process to crash repeatedly. Users will observe Application Error events (Event ID 1000) in their logs.
Affected Systems and Impact
The issue impacts both physical servers and virtual machines, including those running in VMware and Azure environments. The Microsoft Compatibility Appraiser, which controls CompatTelRunner, is a background task that assesses a device's readiness for future Windows updates. Despite the recurring failures and log entries, Microsoft states that device functionality is not affected, and the warnings can be safely disregarded temporarily.
Microsoft Working on a Resolution
Microsoft is currently developing a fix for this problem, which will be delivered in a future Windows update. A specific timeline for the resolution has not yet been provided. This follows other recent Windows Server 2016 issues, including a fix in June for security update failures and a warning last week about application crashes on Windows Server 2025 due to memory management changes affecting apps using Address Windowing Extensions (AWE).
✨ This summary was generated by AI from the outlets' reporting listed below. It is not independently verified and may contain errors — check the original sources. How BrevFeed works →
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Reporting from
Microsoft's August 2026 security update for Windows Server 2016 is causing 0xc0000409 errors and CompatTelRunner.exe crashes on systems with the Compatibility Appraiser diagnostic service enabled. This issue affects both physical and virtual machines, but Microsoft states it does not impact device functionality and a fix is in development.