Export Error

I keep getting an Export Error when trying to copy some playlists to a USB.

It stops and gives me the error but if I go back into the Sync Manager and set it going again it just carries on - I would assume if the error was due to a file not being analysed etc it wouldn't carry on.

I've had it on a few different folders and also different USB drives, it's driving me mad as I have to Sync one playlist at a time and never know when it's going to give me the error.