How do you feel when the server starts showing up these errors every second and keeps on adding core dumps in the root directory of your site? Ask me!!! It took bloody more than 3 hours to trace this issue. The only option I had was, search, search and keep on searching.

Google showed me various things like memory leak to PHP bug, vbulletin showed me same kind of stuff. Reinstalling PHP couple of times did not help. Disabling APC also did not help. (But yes, it was also causing issue on this dual core machine)

Cpanel forums gave me some kind of hope finally, the issue was with Zend Optimizer version 3.0, I quickly disabled it and the problems gone!!!

So if you are also facing this kind of issue on your RHEL 4, just check if you have Zend Optimizer 3.0 is enabled or not.