title: Rhino Mocks gives exception when calling Expect
body: <p>When I run the following test:</p>
  
  <pre><code>[TestMethod]
  public void MyTest()
  {     
      var navigationTree = MockRepository.GenerateMock&lt;TreeOverlay&gt;();
  
      navigationTree.Expect(i =&gt; i.AddExplicitNode(null, null)).IgnoreArguments().Repeat.AtLeastOnce();
  }
  </code></pre>
  
  <p>I get the exception:</p>
  
  <blockquote>
    <p>System.InvalidOperationException: Invalid call, the last call has been used or no call has been made (make sure that you are calling a virtual (C#) / Overridable (VB) method).</p>
  </blockquote>
  
  <p>What does this mean?</p>
  
  <p>Thanks.</p>