Why are these Demo App's blowing out on the call to host.Tracking.Trace() ?

Test method TestProject1.ServiceTest.ShouldInvokeService1 threw exception:
System.TypeLoadException: Could not load type 'System.Activities.Statements.Tracking.StateMachineStateRecord' from assembly 'System.Activities, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'.