The cd player says error and will not play any cd's

A lot of times, cd players will show error, so like all of us, is start putting in all kind of other cd's even music we don't care about, like buck owen's and the bosby twins. Been there done that. Sounds like you have done everything at your end. So, here is what you do and most likely it will solve the problem. At almost any radio shack, best buy store, or stereo shops, they all have little Cd cleaning kits, it goes in like a regular Cd but cleans it, pretty easy and simple to use. Some times its just like putting a couple drops on a blank Cd with some rubbing alcohol and letting it cycle through for a few minutes. I hope it helps, please let me know, so you can get back to rock'n and drive'n
Thanks Mike from fixya.com

In most cases when the CD does not play it is possible that the optical head is a suspect. Sometimes it might pick up ordinary audio CD but will not play other formats. This indicates that the optical head is weak and so there is no detection or scanning of the CD . If the optical is working the tracks will be read immediately but with no scanning the laser head can be defective.
Sometimes certain cleaner disks will not be tracked to run for cleaning as it will not be read and so will reject. Hence it is ideal to manually clean the laser head eye using a cleaning swap /cotton bud with gentle pressure on the lens eye.
If there is no result then watch if the CD spins or tries to spin. If so the board seems to work unless a test is taken on the main board but the possibility of a defective optical head can be the suspected fault.
If any of the above seems otherwise we must recheck with possibilities of a malfunction of the main processor board