Conflict with MSDTC and Windows Server 2008

I have 2 servers (one for applications and another for database) with Windows Server 2008 R2 and SQL Server 2008 R2 .

I have installed an application developed with C # .NET Framework 2.0 and 2 Databases, I use TransactionScope to manage Insert , Update , Delete , if I execute these operations in a single Base of Data everything finishes perfect but if I execute these two operations in the 2 databases I start having problems with TransactionScope .

This conflict does not occur if I install my application on the same server as the Database. I have already executed a MSDTC configuration on both servers but I can not solve my problem, I have the Firewall active, I do not know if this also causes conflict.

Next I add an example of the code that I use for my operations to BD, this code I have it in a method called Executing Sale of the VentaManager class:

using (TransactionScope scope = new TransactionScope())
{

    //El objeto ventasPorUnidadBD ejecuta un insert en la Base de datos "A"
    ventasPorUnidadBD.Insert(objVentas);

    //El objeto inventarioBD ejecuta un update en la Base de datos "A"
    inventarioBD.UpdateInventario(objVentas);

    //El objeto solicitudVentaBD ejecuta un update en la Base de datos "A"
    solicitudVentaBD.Delete(objSolicitudVenta);

    //El objeto movimientoPorMesBD ejecuta un update en la Base de datos "B"
    movimientoPorMesBD.Insert(objVentas);

    //El objeto bitacoraSistemaBD ejecuta un update en la Base de datos "B"
    bitacoraSistemaBD.Insert(objBitacora);

    //Hacer Commit a la transacción
    scope.Complete();

}

When the exception is executed, the next record is generated in my log file:

(06/13/2017 08:03:37 p.m.) MovementPerMesBD.Insert (); - The transaction has already been implicitly or explicitly committed or aborted.

(06/13/2017 08:03:37 p.m.) SaleManager.EjecutaVenta (); - Object reference not set to an instance of an object.

I hope you can help me with this problem.

Thanks and regards.