Violation of security transparency in ScriptManager

I have a .net 4 web app. It was working fine. But two weeks ago an error started happening:
Attempt to access method System.Management.Instrumentation.InstrumentedAttribute..ctor(System.String) in violation of security transparency rules failed. [MethodAccessException: Attempt to access method System.Management.Instrumentation.InstrumentedAttribute..ctor(System.String) in violation of security transparency rules failed.]
   System.RuntimeMethodHandle.CheckLinktimeDemands(IRuntimeMethodInfo method, RuntimeModule module, Boolean isDecoratedTargetSecurityTransparent) +0
   System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent) +482
   System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeAssembly assembly, ...