Invalid call, the last call has been used or no call has been made

Question

I am getting this error when I try to set a mock to have PropertyBehavior():

System.InvalidOperationException: System.InvalidOperationEx

Answer 1

I received this error when I tried to set an expectation on a non-virtual method.

mockedObject.Expect(a => a.NonVirtualMethod()).Returns(null);

The error went away when I made NonVirtualMethod virtual.