How do you change your hold music? can we use a personal CD of music?

Not sure of error code but usually to eject cd knock power off hold eject button at same time you turn power button on, workks for my on cds, computer drives ,etc

Audio books may be different but with a music CD if you press STOP once you can pick up where you left off. Pressing STOP twice reverts to the beginning.

Regular Music CD's and music recorded onto CD-R in Music CD format but NOT mp3

change the battery...

right click on the file u want and click send to and click on the drive ur mpe player is on.

there is a switch that locks all controls

Well first of all, all music purchased from iTunes is in mp4 format, not mp3. You will have to convert you music to mp3 format for it to work. The retail version of nero, works well for that. Another option is to burn your music to cd, then reimport it into your music library, from the cd, as mp3. You'll have to change some setting though if you go that route.

There is a slider button on the bottom of the cd player to take it out of HOLD.

Hope this helps!

Your system will have an input for music. You may have something attached already and so that would need to be changed to what you want. OR you may be using a built-in internal tune. Usually connecting an external source will over-ride any internal music automatically but it may need to be changed in programming. If you connect a new external music system, you can use just about any music device with the right cable. Just make sure it is line-level input (low volume - not amplified) or you can break the music circuit.

is this a digital player or optical one? you can not download music to it if its optical, it can only play disc.