If this worked for all the other DVDs, then these two must just be bad burns. Look for any scratches or such. You might want to try reburning them, and seeing if the problem continues.

I know that when I use Nero, it will give a warning if it detects something wrong with the files (to the extent that it can determine if something's wrong.) Interestingly enough, I burned a DVD with a Video_TS directory (just to hold the DVD files - it wasn't mastered as an actual DVD) When I place it in my computer, it started playing automatically. When I put it in my DVD player, it wouldn't load. Weird.