I can duplicate this. When I switch to 2nd Source via DI6, then I see the "Invalid Data" flash up on the GS3's display. My 2nd Source I just left as "Keypad". This message is due to the GS-EDRV100 continuously reading & writing over the RS-485 serial connection even while the 2nd Source is picked. I know this because when I unplug the serial cable from my GS-EDRV100, the message goes away.
What is your 2nd Source? i.e. what are the values for P3.31 & P4.13?
However, I only see this message when I press the STOP on the display. If I leave it in Run Mode, I do not see this message.