Audio Systems: 04 F150 6 disk problem, plastic tabs, car battery

Question
When I bought this truck, the stereo would display "cd error, eject error, and slots full", so I took that unit out and sent it back to the dealer who sent me another head unit.  I installed it and the same messages came up, so I kept that unit and had them send me another unit.  I installed that today and still get the same messages.  CD error, eject error, and slots full.  I know there aren't any cd's in the unit, so I am lost as to where the problem lies.  Any help would be appreciated.  Thanks.

Answer
when you power the new head unit it needs to be flat on a table or the radio needs to be installed before you plug the car battery also there are to small holes on the top the plastic tabs need to be remove before you install the radio or power the radio