Are you compiling from source, or loading a hex file? Versions of the Arduino IDE beyond 1.6.8 (I think that’s it) have a problem compiling the grbl code. There is a fix if that is your problem.
Read this thread:
Are you compiling from source, or loading a hex file? Versions of the Arduino IDE beyond 1.6.8 (I think that’s it) have a problem compiling the grbl code. There is a fix if that is your problem.
Read this thread: