i'm guessing Rio doesn't support it anmore now that it's in their "legacy" line of players. i ran into the same problem when trying to get my rio500 working. i ended up just scouring google for an hour or two looking for drivers and now that i got them i'm guarding them like gold. just play on google for a while, you won't get any help from Rio. i did find a good file transfer program called RioRio, don't know if it works for the 300 but it's great w/ the 500.