Since release of September 2025 CU for SharePoint Server Subscription Edition we received several reports of application pool worker process crashes with Exception code 0xC0000409 being reported in the event log similar to this:
Faulting application name: w3wp.exe, version: 10.0.17763.1, time stamp: 0xcfdb13d8
Faulting module name: owssvr.dll, version: 16.0.19127.20100, time stamp: 0x689cd397
Exception code: 0xc0000409
Fault offset: 0x000000000033b39b
Faulting process id: 0x32fc
Faulting application start time: 0x01dc37c6ba77ea7f
Faulting application path: c:\windows\system32\inetsrv\w3wp.exe
Faulting module path: C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\isapi\owssvr.dll
Report Id: 5b82605c-4db9-42ec-b10c-6462e8073a24
Faulting module name: owssvr.dll, version: 16.0.19127.20100, time stamp: 0x689cd397
Exception code: 0xc0000409
Fault offset: 0x000000000033b39b
Faulting process id: 0x32fc
Faulting application start time: 0x01dc37c6ba77ea7f
Faulting application path: c:\windows\system32\inetsrv\w3wp.exe
Faulting module path: C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\isapi\owssvr.dll
Report Id: 5b82605c-4db9-42ec-b10c-6462e8073a24
Solution
A fix for the issue is currently in development.
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IS this for a specific SP version (2019/SE)?
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Hi Peter,
this is only in SPSE.
Cheers,
Stefan
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This one issue seems to also affect our Migration traffic (using 3rd party tools). Is there a way to get a more understanding and potential work around. We have already mitigated it for Crawl by pointing to a different Target.
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Hi Joseph,
this issue leads to process crashes for all SPQuery executions against Calendar or Task Lists with ExpandRecurrance property set to = true:
https://learn.microsoft.com/en-us/previous-versions/office/developer/sharepoint-2010/ms469242(v=office.14)
If this migration tool uses such queries to migrate calendar or task lists it will be affected.
Cheers,
Stefan
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Thank you, Stefan. This certainly helps, and yes we are facing this with a task list with some Calendar views.
And by looking at the object Model, this seems to be a runtime issue, but I will ask any how: Is there any way to change any property on the SharePoint View to mitigate this?
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Hi Joseph,
I am not aware of any method to mitigate this – except to skip the relevant lists and migrate them manually.
Cheers,
Stefan
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Hi,
So, the issue occurs for all SPQuery executions against Calendar or Task Lists with ExpandRecurrance property set to = true. Does this include regular user UI interactions? So if they open a task list view it can bring down the W3WP’s?
If yes, is there any resource where we can track the progress of the fix? Because that would mean a huge risk of our farms (SharePoint SE) not being stable.
Thanks and all the best Christmas greetings,
Ruud
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Hi Ruud,
if the view includes a query that expands reccurrances: yes.
To track the fix it will be required to open a support case.
The engineer working on the case can then provide regular updates on the progress.
Cheers,
Stefan
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Hi Stefan,
Thanks for your fast reply! We will open up a ticket. Finger’s crosses no one uses the task lists :).
Best regards,
Ruud