Its been a while for me but I'd check; 1) baud rate at which you are sending. Check it in three places A) in the PC software B) in the system config of the PC and C) in the controller.
2) then check the character you are using for start transmission and end transmission usually a "%" on a line by itself.
3) If I had comment line over 40 characters long it also faulted.
4) My M2 let me have only about 4 seconds between starting the receive side and the sending PC side before it faulted. I looked like Stevie Wonder with one hand on each keyboard as I did a transmission. Never could find where to change that 4 second gap to more time.
Good luck. Let us know how you make out.