Ford Radio w/ 6 CD Changer?

Recently purchased a 2002 Ford Ranger Edge. In the process of tuning up the truck, I replaced the battrery and now the radio thinks there are CD's loaded and when I push the "Load" button it says full and when I push the "Eject" button it says CD Error. Do I have to enter a code or something to fix this? I tried leaving the truck and radio on for an hour as suggested by someone but still no luck.

B
January 2009