i've seen a few MK4 have problems reading certain burned DVDs. some of the time, the problem is remedied by using high quality DVD+R media (not DVD-R) with a slow burn speed and a decent DVD burner. some other times, you're just out of luck.

the unit in my car is a 2005 prod date and reads everything i've given it, even really low quality burns. i was just helping someone with a MK4 upgrade using a 2007 prod date unit, and it wouldn't take one of the burned DVDs that worked in my 2005 unit.

YMMV, but I would at least try a DVD+R from Taiyo Yuden at a slow burn speed and see if that works.