Problem reading some DVDs in player

A friend of mine just bought the Pioneer 16x DVD recorder and burns movies to watch in an old (1999) DVD player. He is using Philips 8x + media and most of the times it is fine, but some specific movies do not play properly, no matter the amount of burns or the burnign speed, while they do play in the PC and in other DVD players.

Could bittsetting to DVD-ROM, or use of (-) media help in this case?