500 internal server error! Reasons this happens?

I am looking for sensible reasons why a dolphin site (7.0.9) would get random 500 internal server errors and what settings should be checked and possibly adjusted to prevent it happening ?

I'm not sure if my errors posted here are related OR would cause 500 Internal server errors: http://www.boonex.com/forums/topic/How-to-fix-these-errors-.htm