Method X has no matching overload that returns Y

Hello,
I'm trying to create a Mock Controller and an instance of that type in order to pass it to my tested class. However, when the mocked method is called I get an Exception:

Test method GestionNet.UnitTesting.UnitTest1.TestDocConfigProvider threw exception: TypeMock.TypeMockException:
*** Method GetDecimales<TipoCalculadorDocDecimales> in type GestionNet.CalculadorDocConfigProvider has no matching overload that returns System.Int32..

The signature of the Method GetDecimales is:

public int GetDecimales(TipoCalculadorDocDecimales tipoDecimales)

And the code I'm using:

MockManager.Init();
MockObject MockDocConfig = MockManager.MockObject(  typeof(CalculadorDocConfigProvider), Constructor.Mocked);            
MockDocConfig.ExpectAndReturn("GetDecimales",  2, typeof(TipoCalculadorDocDecimales));
CalculadorDocConfigProvider docConfig = MockDocConfig.Object as CalculadorDocConfigProvider;
docConfig.GetDecimales(TipoCalculadorDocDecimales.Coste);

What I'm doing wrong? I can't understand why I get this exception.

Thanks,