Have had this happen twice. The first time, it corrected itself.
The second time, I lifted the shredding apparatus off the top, turned it over and brushed off the underside and checked for any jams. I placed the shredding apparatus back on top of the canister and it worked. I have no idea why it started up again, but I did see two small dots that resembles sensors on the underside and I wiped them off.
Dfreecity, October 2009