I am getting this error when trying to set an expectation on an object I mocked that inherits from MembershipUser: ContactRepositoryTests.UpdateTest : FailedSystem.InvalidProgramException: JIT Compiler encountered an internal limitation. Server stack trace: at MockObjectType1.ToString() Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(ref MessageData msgData, Int32 type) at System.Object.ToString() at NMock2.Internal.ExpectationBuilder.On(Object receiver) Here are the tools I am using... VS2008 (SP1) Framework 3.5 nUnit 2.4.8 nMock 2.0.0.44 Resharper 4.1 I am at a loss as to why this would be happening. Any help would be appreciated. Test Class... [TestFixture] public class AddressRepositoryTests { private Mockery m_Mockery; private Data.IAddress m_MockDataAddress; private IUser m_MockUser; [SetUp] public void Setup() { m_Mockery = new Mockery(); m_MockDataAddress = m_Mockery.NewMock<Data.IAddress>(); m_MockUser = m_Mockery.NewMock<IUser>(); } [TearDown] public void TearDown() { m_Mockery.Dispose(); } [Test] public void CreateTest() { string line1 = "unitTestLine1"; string line2 = "unitTestLine2"; string city = "unitTestCity"; int stateId = 1893; string postalCode = "unitTestPostalCode"; int countryId = 223; bool active = false; int createdById = 1; Expect.Once .On(m_MockUser) .GetProperty("Identity") .Will(Return.Value(createdById)); Expect.Once .On(m_MockDataAddress) .Method("Insert") .With( line1, line2, city, stateId, postalCode, countryId, active, createdById, Is.Anything ) .Will(Return.Value(null)); IAddressRepository addressRepository = new AddressRepository(m_MockDataAddress); IAddress address = addressRepository.Create( line1, line2, city, stateId, postalCode, countryId, active, m_MockUser ); Assert.IsNull(address); } } User Class... public interface IUser { int? Identity { get; set; } int? CreatedBy { get; set; } DateTime CreatedOn { get; set; } int? ModifiedBy { get; set; } DateTime? ModifiedOn { get; set; } string UserName { get; } object ProviderUserKey { get; } string Email { get; set; } string PasswordQuestion { get; } string Comment { get; set; } bool IsApproved { get; set; } bool IsLockedOut { get; } DateTime LastLockoutDate { get; } DateTime CreationDate { get; } DateTime LastLoginDate { get; set; } DateTime LastActivityDate { get; set; } DateTime LastPasswordChangedDate { get; } bool IsOnline { get; } string ProviderName { get; } string ToString(); string GetPassword(); string GetPassword(string passwordAnswer); bool ChangePassword(string oldPassword, string newPassword); bool ChangePasswordQuestionAndAnswer(string password, string newPasswordQuestion, string newPasswordAnswer); string ResetPassword(string passwordAnswer); string ResetPassword(); bool UnlockUser(); } public class User : MembershipUser, IUser { #region Public Properties private int? m_Identity; public int? Identity { get { return m_Identity; } set { if (value <= 0) throw new Exception("Address.Identity must be greater than 0."); m_Identity = value; } } public int? CreatedBy { get; set; } private DateTime m_CreatedOn = DateTime.Now; public DateTime CreatedOn { get { return m_CreatedOn; } set { m_CreatedOn = value; } } public int? ModifiedBy { get; set; } public DateTime? ModifiedOn { get; set; } #endregion Public Properties #region Public Constructors public User() { } #endregion Public Constructors } Address Class... public interface IAddress { int? Identity { get; set; } string Line1 { get; set; } string Line2 { get; set; } string City { get; set; } string PostalCode { get; set; } bool Active { get; set; } int? CreatedBy { get; set; } DateTime CreatedOn { get; set; } int? ModifiedBy { get; set; } DateTime? ModifiedOn { get; set; } } public class Address : IAddress { #region Public Properties private int? m_Identity; public int? Identity { get { return m_Identity; } set { if (value <= 0) throw new Exception("Address.Identity must be greater than 0."); m_Identity = value; } } public string Line1 { get; set; } public string Line2 { get; set; } public string City { get; set; } public string PostalCode { get; set; } public bool Active { get; set; } public int? CreatedBy { get; set; } private DateTime m_CreatedOn = DateTime.Now; public DateTime CreatedOn { get { return m_CreatedOn; } set { m_CreatedOn = value; } } public int? ModifiedBy { get; set; } public DateTime? ModifiedOn { get; set; } #endregion Public Properties } AddressRepository Class... public interface IAddressRepository { IAddress Create(string line1, string line2, string city, int stateId, string postalCode, int countryId, bool active, IUser createdBy); } public class AddressRepository : IAddressRepository { #region Private Properties private Data.IAddress m_DataAddress; private Data.IAddress DataAddress { get { if (m_DataAddress == null) m_DataAddress = new Data.Address(); return m_DataAddress; } set { m_DataAddress = value; } } #endregion Private Properties #region Public Constructor public AddressRepository() { } public AddressRepository(Data.IAddress dataAddress) { DataAddress = dataAddress; } #endregion Public Constructor #region Public Methods public IAddress Create(string line1, string line2, string city, int stateId, string postalCode, int countryId, bool active, IUser createdBy) { if (String.IsNullOrEmpty(line1)) throw new Exception("You must enter a Address Line 1 to register."); if (String.IsNullOrEmpty(city)) throw new Exception("You must enter a City to register."); if (stateId <= 0) throw new Exception("You must select a State to register."); if (String.IsNullOrEmpty(postalCode)) throw new Exception("You must enter a Postal Code to register."); if (countryId <= 0) throw new Exception("You must select a Country to register."); DataSet dataSet = DataAddress.Insert( line1, line2, city, stateId, postalCode, countryId, active, createdBy.Identity, DateTime.Now ); return null; } #endregion Public Methods } DataAddress Class... public interface IAddress { DataSet GetByAddressId (int? AddressId); DataSet Update (int? AddressId, string Address1, string Address2, string City, int? StateId, string PostalCode, int? CountryId, bool? IsActive, Guid? ModifiedBy); DataSet Insert (string Address1, string Address2, string City, int? StateId, string PostalCode, int? CountryId, bool? IsActive, int? CreatedBy, DateTime? CreatedOn); } public class Address : IAddress { public DataSet GetByAddressId (int? AddressId) { Database database = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = database.GetStoredProcCommand("prAddress_GetByAddressId"); DataSet dataSet; try { database.AddInParameter(dbCommand, "AddressId", DbType.Int32, AddressId); dataSet = database.ExecuteDataSet(dbCommand); } catch (SqlException sqlException) { string callMessage = "prAddress_GetByAddressId " + "@AddressId = " + AddressId; throw new Exception(callMessage, sqlException); } return dataSet; } public DataSet Update (int? AddressId, string Address1, string Address2, string City, int? StateId, string PostalCode, int? CountryId, bool? IsActive, Guid? ModifiedBy) { Database database = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = database.GetStoredProcCommand("prAddress_Update"); DataSet dataSet; try { database.AddInParameter(dbCommand, "AddressId", DbType.Int32, AddressId); database.AddInParameter(dbCommand, "Address1", DbType.AnsiString, Address1); database.AddInParameter(dbCommand, "Address2", DbType.AnsiString, Address2); database.AddInParameter(dbCommand, "City", DbType.AnsiString, City); database.AddInParameter(dbCommand, "StateId", DbType.Int32, StateId); database.AddInParameter(dbCommand, "PostalCode", DbType.AnsiString, PostalCode); database.AddInParameter(dbCommand, "CountryId", DbType.Int32, CountryId); database.AddInParameter(dbCommand, "IsActive", DbType.Boolean, IsActive); database.AddInParameter(dbCommand, "ModifiedBy", DbType.Guid, ModifiedBy); dataSet = database.ExecuteDataSet(dbCommand); } catch (SqlException sqlException) { string callMessage = "prAddress_Update " + "@AddressId = " + AddressId + ", @Address1 = " + Address1 + ", @Address2 = " + Address2 + ", @City = " + City + ", @StateId = " + StateId + ", @PostalCode = " + PostalCode + ", @CountryId = " + CountryId + ", @IsActive = " + IsActive + ", @ModifiedBy = " + ModifiedBy; throw new Exception(callMessage, sqlException); } return dataSet; } public DataSet Insert (string Address1, string Address2, string City, int? StateId, string PostalCode, int? CountryId, bool? IsActive, int? CreatedBy, DateTime? CreatedOn) { Database database = DatabaseFactory.CreateDatabase(); DbCommand dbCommand = database.GetStoredProcCommand("prAddress_Insert"); DataSet dataSet; try { database.AddInParameter(dbCommand, "Address1", DbType.AnsiString, Address1); database.AddInParameter(dbCommand, "Address2", DbType.AnsiString, Address2); database.AddInParameter(dbCommand, "City", DbType.AnsiString, City); database.AddInParameter(dbCommand, "StateId", DbType.Int32, StateId); database.AddInParameter(dbCommand, "PostalCode", DbType.AnsiString, PostalCode); database.AddInParameter(dbCommand, "CountryId", DbType.Int32, CountryId); database.AddInParameter(dbCommand, "IsActive", DbType.Boolean, IsActive); database.AddInParameter(dbCommand, "CreatedBy", DbType.Int32, CreatedBy); database.AddInParameter(dbCommand, "CreatedOn", DbType.DateTime, CreatedOn); dataSet = database.ExecuteDataSet(dbCommand); } catch (SqlException sqlException) { string callMessage = "prAddress_Insert " + "@Address1 = " + Address1 + ", @Address2 = " + Address2 + ", @City = " + City + ", @StateId = " + StateId + ", @PostalCode = " + PostalCode + ", @CountryId = " + CountryId + ", @IsActive = " + IsActive + ", @CreatedBy = " + CreatedBy + ", @CreatedOn = " + CreatedOn; throw new Exception(callMessage, sqlException); } return dataSet; } }