I have this same issue with Jamming and error2. I did install everything correctly and was already on my 2nd roll. Somehow it randomly got stuck/jammed it seemed. So I tried to clean the clamps on the bottom, made sure it was rolled tight and all parts are in correct placement. It seemed to only move a bit if I gave it a nudge but I can tell the reefdrive unit motor was not working properly.
Even with nothing attached I tested the reefdrive unit and it did not move. So I contacted Red Sea and went back and forth a little and they sent me a replacement drive unit. I swapped it out and works perfect again. I am sending them the bad drive unit back.
Not sure if this helps but just sharing my experience. Good luck…. Btw I was stressed out too because I modded my sump as well. I was manually just rolling the mat every chance I could while waiting for replacement which was a pain. Basically just flooded the sides of the reefmat most of the time causing different issues for me.