There are two possibilities - corrupt DB or songs in wrong format.
If it is a corrupt DB, then go to RCA's website for the latest firmware upgrade.
Make sure the songs are in the correct format. Make sure the songs are not AAC, WAV, streaming, or some other non-supported format
Mp3 players are more complicated than ever. This player may only accept DRM-encrypted WMA files. I would first check the songs that you have downloaded to make sure they did not have "temporary" licenses with a fixed end date. You can do this by right clicking on an individual song, clicking on properties, and selecting the "license," "digital rights mgmt" or "media usage rights" tab - the wording varies by configuration. It will give you info on the license. If the song says that it has no license, it will not work with this player. One remedy is to use mp3 converter software to convert all of those wma files to Mp3's - I don't know of any free ones, but you can certainly look for free Mp3 Converters. Another remedy on unlicensed songs is to hit the "acquire license" link in the license tab, if one exists.
-Tha Mp3 Doctor