JVC. KD-G721 Car Radio: Why are some MP3 tracks not always recognised?

JVC. KD-G721: Sometimes some of the MP3 tracks on my memory sticks are not always recognised. Other times they are! Ideas anyone? Are there 'drivers' (dll) for the software on this JVC Radio, CD & MP3 Player? If so, where do I find the updates and install them? Last thing... The display says "DAB Ready" - I don't have the Manual (lost it in recent house-move) How can I setup the DAB? Any help &/or guidance very much appreciated! Many thanks in advance.