These presenters can often jam due to several reasons, either the trim on the end of the presenter arm (the loop the belt goes through) can bind inside the interior trim, or someone will just decide it's a play toy and hold their hand in front of it, thus stalling it.
When either of these events take place, there is a force limiter inside the motors (or possibly part of the control unit, unsure which) that will shut down operation of the presenter.
I believe the force limiter is reset much the same way the 140 chassis door latches are reset; by removing the fuse momentarily.
I checked out the wiring diagram for the cabriolet, it looks like if I had to pick just one fuse to try removing for 10 seconds or so, it would be fuseC in the main fuse box, this is circuit 30 to the control unit. Also of course make sure the fuse isn't blown. OTHER fuses to check would be fuse 1, 5, 9 and also fuseB. These fuses you could also try pulling for 10 seconds also to see if they reset the control unit, but C would be the one I would suspect would cure the problem if indeed the force limiter needs to be reset.
Also inspect the presenter arm ends to see if they just fit flush to the interior trim, or if they appear inset too far and possibly are jamming under the trim.