I had this same issue after getting a paper jam almost two weeks ago and tried everything to get rid of the error message including leaving it unplugged, all covers open for 48 hours...
I FINALLY found the answer on fixya.com
http://www.fixya.com/support/t1168748-document_jam
Solution #2 worked for me:
I left my machine on while I opened the paper feed tray, manually twisted the middle feed roller a few times, then closed the cover and the message disappeared. Good luck!
HappyFaxing, March 2011