NOTE – This has been fixed with the MS14-053 update.
Install KB2966828, and restart (that is the awesome PSWindowsUpdate in action):
I’ve also encountered it causing issues with starting ASP.NET app pools and causing failures while running iisreset. A quick workaround is to add the public key token that is failing (b03f5f7f11d50a3a, found while debugging the crash) to the registry in the strong name validation bypass list:
Adding that will allow things to work again, until the problem is fixed by Microsoft at some point.