Xperia Mini/pro :: Music Files Won't Play

I am a relatively new user to this phone, and so I have been trying to get my music files (mp3 format) onto my phone.I have bought a new 32GB sd card to load them on, and some files will play, but most state they can't play.I have tried a transfer using file copying, and also used MediaGo, but I still get similar results.The mp3 files play correctly on my computer (Windows Media Player) and on my iPOD, so I think the files should be ok.Are there specific sampling bit rates needed for the Xperia?Further to this thread, I have now ripped some original cd's in various formats and bit rates (Mp3 to WAV), and it makes little difference to their ability to play. Some do, but mostly they don't. I can't find any common factor.

Finally getting somewhere .... I think there is a problem with the new 32Gb MicroSD. Its rated class 10, so its maybe faulty or too fast???I replaced the sd with the one that came with the phone, which is 2Gb (no class stated), and everything plays fine with this.