Error 500 / Server crashes when running PHP on one domain

[Lumio]

Hi,
sometimes I get Error 500 when navigating on a domain. When I check the logs it tells me, that fastcgi didn't quit properly. So I checked the domain and there are several core.* files with crash-information
The good thing is: after reboot it seems to work again. But I would like to know how I can solve that problem, because I have that all few weeks/months.

And maybe someone knows how to analyze thos core files?

Thanks