updating m100 firmware without a gimbal

Hi everyone, I’m having a problem with my DJI Matrice 100 and was hoping someone here might be able to help. This occurred after failed firmware update using dji assistant 2 ,then after restarting the drone started beeping non stop and these errors appeared Errors: Main Controller connection...

I've got about 25 flights on my new M100 (no camera mounted yet) and decided to update my firmware. I downloaded both the DJI Assistant 2 and WIN driver. Then I tried to update the firmware following the M100 user guide instructions on page 48 (no gimbal - plug in above the aircraft indicator...