Hello there,
Hope I could still share with you this fix because this is where you need to look at when you think you have done everything to remove the paper jam.
1. Turn off the printer and pull out all plugs and power cord that is attached to your printer.
2. Remove the paper tray at the bottom and let the printer lie at its back so that you can see underneath.
3. Get a flashlight and look closely for the sensor located underneath the printer. The sensor is located in a small
square hole, just above the small black plastic "lever" (looks like a small hockey
paddle) on the left side of the gray rubber roller. Move the lever so that you can freely look closer on the hole.
4. Notice because there could be a tiny paper shred stuck inside and this causes the sensor to detect a paper jam.
5. Get a small tweezer to remove that paper out.
6. Next, let the printer stand normally and return the tray back.
7. Re-plug all cables and start your printer. That's it!
You can also click on this link for this trick.
http://www.fixya.com/support/r3827902-canon_imageclass_mf3240_paper_jam_fix