I've noticed that on occasion with bad / incompatible media. Try the disk in another player if you can, maybe that one has better luck. I'm often satisfied it at least one of my players will play a disk I made. I figure then the data is there and if I need it later on I can rip and burn a new one. I doubt I'll ever live long enough to watch most of these things anyway.
Do you notice it more at the ends of the movie? My bad media tends to screw up on the outer edge of the disk more than anywhere else.
There's no way that I've discovered to determine what is good media for yourself without trial and error. But once you find a batch that works, try to load up on it. I have a memorex branded lite-on that works great with the memorex branded dvd's (cool colors version ... Ritek r03) but not so good when I bought a sale priced 50 pack of memorex branded (gray ... verbatim mcc003) dvd's ... even though the verbatim mcc003's were supposed to be good disks.
Also, It doesn't help that you have to buy the dvd's before you know what's inside them. It's not like the package tells you.