Modicon quantum communications

i m using Modicon Quantum 424 PLc and try to connect my PC with modbus port but i m getting an error.. Bad Response Checksum Error 120 wat does it means.
when i monitor this through modbus tester code is recieving from PLC but with error.i made the cable according to the drawing and using the right setttings (RTU 9600, Even, Data bits-8,stopbit-1,flowcontrol -none) but still i m getting the same error.
what is the cause of this problem.

Regards,
khalid

Are you getting this error continuously or intermittently? Do you ever get good communications? It may be the cable has a loose connection, or you may have a noise problem, or you may have different parameters for parity and such.

A little more detail, please.

yes i m getting the same reply again and again .........

01 illegal function.....
modbus LED is blinking...........,
i checked all the connections of cable

PLC PC
1 5
2 3
3 2
5 5
4 6
6 4
7-8jumpered on both the sides.i have some doubts regarding cable.
can u verify......