I'm so glad someone else has had this problem! I've had 2 copies of this disc, purchased by separate teachers 6 months apart, and neither will play. It must be a dodgy batch of discs. Our solution was to use MakeMKV to rip the main movie off the disc, then burn it as a file onto a new DVD and call it 'backup copy'. That works fine. The copyright's a bit of a grey area but I reckon as long as the copy is kept with the genuine disc it's OK.