2015 gem error code 51

Hi Oldhouseboater’. You may remember I’m the guy who sent you a free 7.5 motor with a damaged armature a couple of years ago. Now I need some help. I bought a 2015 Gem. In a senior moment tried to move it with the charger still plugged in. It jerked suddenly, then died with a code 51 showing. Tried shutting off main power for 1 hr, no cure. Have full 72v on batteries.
Hate to take it to the dealer except as last resort. Any suggestions, or, where can I get a copy of factory manual or troubleshooting guide so I can try to fix. Hoping it’s something simple, bad breaker, fuse, etc.
Thanks, Mike

Manual sent…