RNS510: random play at root level folder

[jmj]

I recently purchased a VW with the RNS510 unit. I managed to load songs onto the hard drive arranged within several folders and sub folders. However I can't figure out how to random play songs (Mix) across all subfolders of a root folder. For example if I have folder A with sub folders B, C and D, I'm unable to play random songs at higher level folder A.
For some reason when I play folder A and then select "MIX", only songs within sub folder B are played (given folder B is first off the rank).

Anyone able to help?, or is this a limitation of the RNS510 unit.

[Maverick]

You need to only have one top level folder.

http://www.my-gti.com/167/volkswagen-rns510-loading-of-mp3s