Stored Procedure And Transaction

I have a function in which I use a stored procedure and a transaction.
I use the following code, but I get the exception e (last try-catch): This SqlTransaction has completed; it is no longer usable.
(btw, the SendEmail function currently returns False, so the transaction should ALWAYS roll back)

    Public Shared Function SaveGBEntry(ByVal myGBEntry As GBEntry, ByVal Language As String) As Boolean
        Dim bSuccess As Boolean = False
        Dim MyConnection As SqlConnection = GetConnection()
        Dim cmd As New SqlCommand("spNewGBEntry", MyConnection)
        Dim fBeginTransCalled As Boolean = False
        Dim myTrans As SqlTransaction
        Try
            MyConnection.Open()
            myTrans = MyConnection.BeginTransaction()
            cmd.CommandType = Data.CommandType.StoredProcedure
            cmd.Transaction = myTrans
            fBeginTransCalled = True
            Dim UserCodeOwner As Integer = UserFunctions.GetUserCode(myGBEntry.UserNameOwner)
            Dim OwnerEmail As String = UserFunctions.GetUserEmail(myGBEntry.UserNameOwner)
            cmd.Parameters.Add(New SqlParameter("@UserCodeSender", myGBEntry.UserCodeSender))
            cmd.Parameters.Add(New SqlParameter("@GBText", myGBEntry.Text))
            cmd.Parameters.Add(New SqlParameter("@GBUpdateDate", myGBEntry.UpdateDate))
            cmd.Parameters.Add(New SqlParameter("@UserCode", UserCodeOwner))
            cmd.ExecuteNonQuery()
            myTrans.Commit()

            If MailFunctions.SendEmail(myGBEntry.UserNameOwner, OwnerEmail, ConfigurationManager.AppSettings("emailINFOname"), ConfigurationManager.AppSettings("emailINFOAddress"), True, "NewGBEntry", Language) Then
                bSuccess = True
                fBeginTransCalled = False
            End If
        Catch ex As Exception
            GlobalFunctions.ReportError("GUESTBOOKDAL:SaveGBEntry", ex.Message)
        Finally
            If fBeginTransCalled Then
                Try
                    myTrans.Rollback()
                Catch e As System.Exception
                    GlobalFunctions.ReportError("GUESTBOOKDAL:SaveGBEntry", e.Message)
                End Try
            End If
            MyConnection.Close()
        End Try
        Return bSuccess
    End Function