A quick heads-up on Windows Server 2012, Fail-over Clustering and KB2750149, an update for the .NET 4.5 Framework. This hotfix was released on the January 8th, 2013.

After installation, this hotfix will break the Windows Server 2012 Fail-Over Clustering MMC Snap-In, resulting an error when navigating stating:

A weak event was created and it lives on the wrong object, there is a very high chance this will fail, please review and make changes on your code to prevent the issue.

Microsoft is currently investigating the issue. Until then,it is advised not to apply KB2750149 on Windows Server 2012 Fail-over Clusters or uninstall it when you are experiencing the issue.

Note that the Windows Server 2012 Fail-over Cluster will keep working, as well as the related PowerShell cmdlets (another reason to start using the shell instead), it’s just that the cluster can’t be properly managed from the MMC.

Regarding Exchange 2013 DAG, which can be build on top of WS2012 Fail-over Clusters, you shouldn’t notice the issue because fiddling around in Fail-over Cluster Manager is a no-no for Exchange DAGs. Nevertheless, I’d recommend following the advisory and not install or uninstall the hotfix until further notice.

More information in this and this topic on the TechNet forums.

Update (23jan2013): Hotfix KB2803748 fixes the MMC crashing issue. It’s available through Windows Update or download it directly from here.