I'd check the DVD to make sure it is free of scratches, fingerprints, etc. If so, you may have a bad spot on the DVD. Could also be the drive, but with it being just one section of the maps the DVD would be my first suspect. If it is an easy error to duplicate (maybe by manually moving the focus of the map over to the trouble area?) you could show the dealer and see if they'll swap another disk in to see if that fixes it.