music suddenly not working

[cruisertrek]

I have a 1st generation droid, with 700+ songs on it. 36 of them are Bon Jovi. 2 days ago, half of them stopped working-a message comes on the screen and says, "this music file is not supported by this device", or something like that. Anyway, 2 days ago, those songs worked. I've deleted the files off the phone, and then re-loaded them, with the same result.

Does anybody out there have any idea what's going on, and how to fix it?

Thanks.