replicated dvd

all,
i authored a dvd, sent the dlt to the rep. house and now the dvd has shipped...

we've gotten some reports that the dvd is acting funny at certain points...all of which were encoded at medium bit rates and has worked on every dvd player i've tested as well as the players at the rep. house.

i used dvdsp...and i'm completely stumped on why this is happening...i'm thinking possibly the dvd is damaged or scratched or lest likely, their player is acting up...

any ideas?