this may be a dumb question, but is it with all DVD's ? We have some DVD's that act weird and are not playable in the front DVD. If it is on all DVD's there may be a problem with the dash unit. PErsonally I would handle this repair myself calling / emialing "Vinh" thorugh customer service. Changing the in dash unit will be easy.
We added a small Sony BluRay to the TV in the front which works better for us and the kids.
Little trick, you can play the audio only from the big TV through the coach sound system. Jayco fed the dash radio with an audio signal FROM the TV. You just need to set the TV audio out to "fixed" level from variable, so you can hear it properly.
On the road they use the TV with the Blu Ray disc player and TV set to variable. The wife and I can then use the dash radio, nav etc inpedepantly form the kids.
When watching movies while parked camping, we change and use the audio from the dash which sounds much better and can overcome the air conditioner rnoise