dvd

I just bought this http://www.caraudiocentre.co.uk/product.asp?product=20856 I really like it but i thought you cud play dvd mp3 discs on it. However it rejects the disc. Does anyone know if there is away round this. I dont understand why it wont play it as it plays most other dvd...

will be after a dvd head unti after xmas (jan sales:D ) seen kenwood kvt627 but no t.v in it so for an adaptor it £250 am i rit in thinking u need for a good dvd play is: 2 AV inputs or u can put a cd changer on it ect..... 1 av outputs so u can hook up to other screens( if u wanted 2...