there are 2 posibilities.
1 you have a bad senser and it needs repair
2. there actually is a paper stuck someplace but its very small and hard to find. The last time i had somebody with this problem they swore there was nothing jammed. I had them go in with a big flashlight and they found it and got it out with i think it was a butter knife and tweezers. and it worked perfectly afterwards.
so definately try a flash light and look closely. The fact that it says rear door means its probably towards the back. It might be stuck under the fuser where its very difficult to see.
actually it is the inside of the rear cover. But if you have a duplexer installed it would also cover the duplexer
Still same error. Already used a flashlight before I enlisted your help. Already took all of the parts off to get a clear view of the path of the paper. No obstructions whatsoever. That's when I concluded that maybe there was a way to clear the error. I also restarted it. Still same error. Sorry, but there was nothing you said that I hadn't already tried. So, actually, you were professional, but nothing you said helped. THank you those.
If it has a duplexer unit on it check that. If it does NOT have the duplexer on it there might be a small switch or a setting in the control panel which tells the printer there is a duplexer. Make sure that is set properly. Make sure that the cover is closed properly. The inside of it seems to be part of the printer feed mechanism so it will be sensitive if that part is loose or blocked or damaged.
Otherwise if you are sure that there is nothing there its quite possible there isnt. Restarting the printer should clear all the error messages. If you see it go through its posting routine prior to starting its clearing them. The error is not stuck its turned off and comes back on when it does its system check. That means a bad senser. Its not an expensive repair but it needs to be repaired.
There is a limit to what i can do from here. i cant go there and fix it. If it was a user servicable part i could tell you where to purchase it. The best i can tell you is that it is one of the things i have gone over with you or its a bad senser. and it needs to be repaired. That should at least give you the satisfaction of knowing that you tried everything possible and you know what the problem is. Is that worth something to you ? You still pay your doctor if he examines you and says "this is your problem but you need to see a specialist to have it treated"