It is possible that the caddy is sticking, does the caddy front cover have a small circular hole in it where something like a straightened paperclip can be inserted, if yes then this is how you manually eject the caddy.
If the above is not an option try a factory reset "how to" below;
1.Using the supplied remote, press the Home button.
4.Select Reset to Factory Default Settings.
5.Select All Settings.
If neither of the above helps and the player is covered by a warranty I would send it in for repair.
Good luck and let us know how it goes.
NB: I moved your topic to the hardware forum due to the nature of the issue + more people are likely to read the topic and someone could possibly suggest something that I have not.