I copied over my music library (all m4a files) and it worked well. However I noticed that with the Music tab I was seeing duplicates of all the songs - one file didn't work, the other file would play.

When examining the drive I noticed each song had a corresponding  hidden 4kb file associated with it, the filename starting with "._". So I deleted all these - duplicate entries are now gone. However I'm now unable to play any of the songs from the Pogoplug, either through the web or through the desktop client. I've tried rescanning the drive with no luck. I'll probably delete the folder and re-transfer it from my PC.

I should add through the web interface my songs now show as type 'application/octet-stream' rather than 'mpeg4 audio'.