Denon UDM5 CD trays will not open or play

[KT]

I have a Denon UDM5 small stereo system. None of the three CD slots will open. Last week I put a CD in each one and it played find. This week nothing, just flashing lights on the 1, 2, 3 and "ERR' shows on the display. Can anyone help me? I do not any manuals to reference.
Thank you.