I have been trying to comunicate my Laptop with the PLC by means of a PC adapter (rs 232 to MPI)
P.N. 6ES7 972-0CA23-0XA0. and seems to be impossible, it always send the 33:17106 failure

The funny thing is that with the old PC adapter I have no trouble.

 

I'm useing a new one and I have no problem.
Maybe you should compare boud rate selector (on side of the adapter) with seting in PG/PC Interface.

 

I Know that there are 2 different types of adpater. One is OCA23 and the other one is OCA33. One is for null modem and the other one is for full modem, but which is which i don't remember. this may be a problem. The other problem may be in the PC/PG interface where you did not select the right communication rate for the adapter. There are two communication rate, one is 19200 and the other is 38400 i think. If you are set on 19200 change to 38400 and maybe it will work.