Here's the screen shot of my flow chart. You cannot see all if it 'cause there are links that fit off the screen (they all work flawlessly). I have captured the part where the problem is, the first or more accurately the second play. My clients copy will not play from the main menu. I wonder if the issue might be that link is only set from the copyright menu to the main menu and not the play button as you can see in the image capture. I have had trouble with Encore crashing when I have previewed from the copyright menu forward. Yet when I would burn the disk it would play properly on my BluRay machine. 
I have modified my set up in my encore flow chart so that both the time out on first play of the copyright screen and the skip button both link to the play button on the main menu. I have not made a new copy of the DVD yet to see if that will change how my Windows media and Classic Media players on Vista play the program. But with it set that way it previews without crash and to the play button highlighted in the main menu in Encore preview.