Error with RecorderExpectations when debugging

I'm getting an error with the RecorderExpectations while debugging and stepping through the code.

Here is my code block

using(RecordExpectations recorder = RecorderManager.StartRecording()){
            recorder.ExpectAndReturn(ApplicationScope.Settings.MailFromServerAddress, fromEmailAddress);
         }

As soon as I get to the closing bracket on the using block, an exception is thrown. Here is the exception :

TypeMock.TypeMockException:
*** Cannot mock types from mscorlib assembly, or no return value set..

This is the stack trace:

   at TypeMock.RecordExpectations.Dispose()
   at GameFly.Retail.UnitTests.Infrastructure.Mail.SupportSmtpEmailSettingsTest.FromEmailAddressFromSettings() in C:DataProjectsGameFlyRetailMainLineSrcGameFly.Retail.UnitTestsInfrastructureMailSupportSmtpEmailSettingsTest.cs:line 93

If I run the test out of the debugger or dont step into the recorder.ExpectAndReturn code block, everything moves on as planned. I also have almost exactly the same code in other tests but they just access a different setting of my settings object and they work fine.

I am having a differnt problem with the same set of tests but I believe they are unrelated so I will create a different post for that.

Thanks.