Bearshare is slightly out of my territory. Try highlighting/selecting one of the mp3's & select which mp3 player you want as the default to play it. Then try playing/launching them again. If still no luck, then either your mp3 player is lacking the codec to play it or it's incompatible or it's corrupt. eg: it could be Ogg Vorbis or other that your player doesn't recognise or it could be an m4a (mp4) file. Just to find out, try using QLC (it's free) which has heaps of plug-ins to play all types of mp3. Try it & see if it makes a difference. If yes you might want to make it your default mp3 player. I'm not sure whether it can play m4a files or not. WinAmp 5 & Nero 6 can.

See how you go.