RS232 to MPI convertor

Hi Hamid! You need the SIMATIC S7 PC Adapter with part number 6ES7 972-OCA23-0XA0. This will convert MPI (from the PLC) to RS-232 (of your PC). We've been using this a long time ago...
I am having a problem on the RS232 - MPI connection. On one application it is not working at all and I really don't where the problem is coming. Could anyone help?