NET Patch breaks SCCM (KB2840628)

I had an interesting day this week, we were preparing to apply CU2 to our SCCM 2012 environment and I was applying it to our test environment. The Site Server and SQL server patches went well, and then our clients had a hickup, but after an hour, they went on with no issue. Then I went to apply the patch to the admin consoles. They got stuck in the 0% download and never left. Obviously, CU2 had broke something on our site, it was the only thing that changed! Well, after some initial looks around the logs and attempts to get this thing going, we noticed the MP-Location logs had an interesting error..

ErrorLog from Maintenance Mode Error
ErrorLog from Maintenance Mode Error

Come to find out, the .NET patch (KB2840628) was applied to our SQL server, which causes just this issue. We had dealt with this in production but I had completely forgot about it in our test environment! So I had worked for several hours on this problem only to find out, it was something we had already dealt with! I’ll never get that time back….