Could be a bad rip -- what file extension is showing up at the end of each track? Anything strange like fla~ instead of .flac?
Will the files be permanantly residing on the USB drive?
One thing simple to try to see if it has something to do with your USB .... copy the contents of one album to your HD somewhere. I'm assuming that the trakcs will be under folders \AlbumArtist\Album\.
Import=>Import Single folder and see if it works.
