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Windows 11 update: .NET Framework bug causes apps to crash

Microsoft warns of a new bug in Windows 11. With the optional update KB5012643, which came out at the end of April, there are problems with apps that use certain parts of the .NET 3.5 framework. This is according to a new listing at Microsoft Support. With the known issues that Microsoft has in the Windows Release Status Dashboard documented, you can now find the exact information about the problem (via ONMSFT Microsoft just fixed safe mode issues that appeared with the KB5012643 update. However, there is still no fix for the new bug. Instead, Microsoft recommends that everyone involved uninstalling the update again.

Since this is an optional update, there’s still hope that not too many will be affected at this point. Also, unlike the safe mode issue, Microsoft has not yet rolled back this issue as a known issue to bring users back to a bug-free version. How widespread the problem really is is unknown. The error occurs in connection with applications that use components of the .NET 3.5 framework. The group has not disclosed in detail which apps are involved. The error causes the applications to fail and crash. Microsoft has announced that it is working on a fix that will be available as an update in one of the next releases.

Microsoft support says:

  • Error description: Some .NET Framework 3.5 applications may have issues
  • OS Build 2200.652 / KB5012643
  • After installing KB5012643, some .NET Framework 3.5 applications may experience problems or fail to open. The affected applications use certain optional components in the .NET Framework 3.5, eg, For example, the Windows Communication Foundation (WCF) and Windows Workflow (WWF) components.
  • Workaround: To fix this issue, you can uninstall KB5012643. To do this, click the Start button, type, and select Windows Update Settings. In the Windows Update Settings window, select View update history and then select Uninstall the update. Find KB5012643 in the list, select it, and then choose Uninstall.
  • If you are unable to uninstall KB5012643, you can also resolve this issue by re-enabling .NET Framework 3.5 and Windows Communication Foundation in Windows Components. See Enable .NET Framework 3.5 in Control Panel for instructions. Advanced users or IT administrators can do this programmatically by using an elevated command prompt (run as administrator) and running the following commands:
  • dism /online /activate-feature /featurename:netfx3 /all
  • dism /online /activate function /functionname:WCF-HTTP activation
  • dism /online /enable feature /featurename:WCF-NonHTTP-Activation
  • Affected platforms:
  • Customer: Windows 11, version 21H2