Sorry to cut in with what might be interpreted as a "me too", but in looking at my own site (also on Starka), I've noticed that the problem is intermittent -- sometimes I get a page render, sometimes a 500. The PHP on my site is restricted strictly to includes (there is no "active" code), and I am not using .htaccess to do anything at all (no rewrites, etc.). It may be an indication of a fault in one server in the cluster.
That's as close to a diagnostic as I can get, since I have no more access than the run-of-the-mill user.