Why won't my Roomba run on carpet?

My Roomba 671 runs great on wood floors, runs on my tile and carpet at my house, but when I take it to my "gym room", it will only run for a short time on the padded workout carpet. The carpet is dark gray. We have tried three other iRobots and we get the same results. Runs for a minute (or a couple minutes), gives an error 10. We clean the wheel cavity (sensor area) and don't find any dirt.

Could this be a "black carpet issue"? Do I need to block the sensors?