ChilliPeppr throws error:'Expected command letter' after about 32 codes

I am running ChilliPeppr on Win7 64bit desktop. It connects OK and successfully processes 32 gCodes. Upon addition of the next code - regardless of its nature, like the basic G1 X5, - it throws an error :'Expected command letter.

This happens with my own gCode but also - I can carve a test project in Easel, But if I export gCode from this project and send it via ChilliPeppr only the starting part of about 30 codes is executed, followed by the same error.

Please advise. Thanks in advance.


Issue resolved by setting the option for Arduino on COM3 to grbl. This option is not available prior to the connection but appears afterwards.
Now all works fine.
Still I would appreciate if someone could clarify the correct procedure of connecting given Communication Port on COM1 and Arduino on COM3.