This issue was raised in this forum quite a few times already. If you use the [Search] button you will find it easily.
The best solution is to resync the subtitles (which often come from a different source than the movie). I personally use (and very much like) "subsync" which you can download from Vladimir's site at pandora belgium.
E.g. see:
http://forum.bsplayer.org/viewtopic.php?p=5958#5958