I've read a solution here as follows:
"try using scotch dvd player cleaner and/or clean laser lense with alcohol;highest percent posable and/or the optical pickup needs replacing and/or faulity or failed modifications; and lubricate tray rods if it plays and stops or skips; use a lightweigh oil; like 3 in 1 oil."

What I'm wondering is - has anyone tried anything like this for the wrong disc error and did it work?

Mags, June 2006

I pushed the carriage all the way up to the middle and then put a clean disc in 3 times. Low and behold it worked. Now if I can get the battery compartment cleaned from the leaking batteries.

Carol, March 2017

I´ve done everything and the problem remain. From my point of view the player is blocked and there must be some unlock code. My DVD player is Nakay NJ-618DVD

gilberto@cubatel.cu, September 2008

Here was my fix. My son has a coby dvd player--"wrong disc" message. cleaned the lens, same error message. had nothing to lose. took it apart. thought of corrosion on jumper switches. pulled all of them off and put them on two or three times. Had this problem with a nikon flash once. This fixed it... works like a champ.
You will need a small screw driver, check to see the type of screw heads, to detach the bottom and expose the circuit board; and a pair of needle nose pliers to remove and reinsert the jumper switches. Make sure no electricity is running through the unit. good luck, hope this helps.

Kirt, July 2008

Thanks for the advice Mags, I've just done the same trick with my 3 year old sons cd player, which only needed a clean.

Hugh

Hugh Duffy, October 2006

I'm answering this question myself, just in case anyone out there needs the answer. We (gently!) used a cotton bud dipped in a little alcohol (Stolichnaya vodka to be precise) to clean the laser lense and the wrong disc error has disappeared, the dvd player is now playing discs again.

Mags, June 2006