I'm hoping Dan, Alfie or Richard will comment but in the meantime do you have a seperate DVD unit in the rear of the vehicle dedicated to the navigational DVD?
If your COMAND can play, or should play Mp3's then I would guess what works on one 'should' work on another and we will loose nothing by trying.
I can only recite the way I do things and it has never failed.
1. I gather my Mp3 files into the relevant folders.
2. Make sure you only have Mp3 files No playlists, no text files
3. Make sure there are no more the 255 files, or 255 folders
4. Make sure there are no empty folders, or folders that do not contain Mp3's
5. Write all the folders onto the root of the Cd or DVD
You can if you want, put 255 files onto the root of the disc but any files that are not kosher Mp3's might cause problems. Mucking about, or fine tuning the Mp3's might cause problems.
I use Nero Express Data CD\DVD with all the default settings and touching wood as I type, it never fails. There is other CD writing software that can be used and I'm sure it gives similar results, I have a method that works and am happy with it.
If you are doing this and your still getting problems then please pm me.
Regards
John