I've had this before and can't remember how I solved it, but has anyone else got any advice please? I've been mucking around (yes I know!) with where my music is stored and how I access it. A while ago I put all my music from my old PC onto an external hard drive and got iTunes on my iBook to access it from there. Recently I've been trying to get iTunes to see the library via Airport Extreme to which the hard drive is connected. On some songs, and this is now the case if it's via the Airport or connected directly, I get the following message... "The song "Name of Song" cannot be used because the original file could not be found. Would you like to try and locate it?" When I *do* try and locate it, it's there but the extension is .m4a - which don't play, .m4p plays fine. Why are some m4a and some m4p?