Hey guys, I am trying to upload Ardurover 3.3 into my Pixhawk, but i keep getting this error message. 
I had found a similar problem recently when trying to install Copter-3.5.7 on a board but @meee1 fixed it. I’ve just tested loading Rover-3.3.0 on a pixhawk1 just now (I had to choose No for ChibiOS because this is an invalid option because we didn’t support ChibiOS back then)… but then it worked. Can you try again after first updating the MP? It can be updated by opening MP, click on the Help button on the top and then either “Check for Updates” or “Check for BETA Updates”