Duplicated bytes in serial port

I’m trying to connect a RTU to a Scada using the TS MEI, the main comunication is RS-232, 9600,8,E,1 and using a IEC protocol. The problem is when the RTU (or the Scada, it depends of the data send) sends a byte 0xFF, in the other extrem i receive 0xFF 0xFF, and this causes crash of the comunication.
Another problem is when i transmit the couple of bytes 0x0D 0x0E in the other extrem i receive 0x0D 0x00 0x0E.

Excuse me for my terrible english.


I forget yo explain the hardware configuration.
The RTU and the Scada uses RS-232 communication, with no handshake, the ip communication is over a VLAN, and the two portservers are configurated like tunneling.