I recently had a paper jam problem with the Canon ImageClass MF3240. I followed all the possible fix to remove the jam, but after clearing the paper in all access doors, the printer still gives the paper jam error. Restarted the printer several times to no avail and the red light keeps blinking. Well here is something not suggested in the manual.
1. Turn off your printer.
2. Pull off all plugs attached to your printer back.
3. Remove the paper tray to look for the sensor located underneath the printer.
4. Get a flashlight and look closely. The sensor is located in a small hole, just above the small plastic "lever" (looks like a small hockey paddle) on the left side of the gray rubber roller.
5. There is a tiny paper shred stuck inside and this causes the sensor to detect a paper jam.
6. Get a small tweezer to remove that paper.
7. Return all cables and start your printer and that's it!
Hope this helps you as it saved me a big headache.