Try this if you haven't already. Turn off main power, unplug machine wait a couple of minutes. Fire it backup see if it will reset. I have a SP300V and when weird stuff happens its what I do.
Yeah I've tried that, it works most the time but I was wondering if there was a more permanent solution.
My GX 24 was having the same problem. According to service center one of the pinch rollers was bad. They repaired it no trouble since. The pinch roller sensor works by way of magnets.