Exception: System.ServiceModel.ServiceActivationException: The service ‘/SecurityTokenServiceApplication/securitytoken.svc’ cannot be activated due to an exception during compilation. [solved]
Microsoft Update MS13-004 and SharePoint 2010 running on Windows Server 2008 RTM causes SharePoint to not function. If you installed the patch, uninstalling [KB 2756920] will fix the problem. You can also install Service Pack 1 to reslove the problem. It is a known issue which also affects other products like Exchange 2010.
Further information can be found here: