One of the servers here at work was giving a 500 Internal Server error whenever a PHP page was loaded. Among the various things that can cause this error when you’re running PHP in CGI mode (suPHP), this error showing up in the Apache log was most unusual. Turns out it’s due to the suphp binary missing its sticky/suid permissions.
SecurityException in Application.cpp:188: Do not have root privileges. Executable not set-uid root?
To fix, simply chmod +s the suphp binary:
chmod +s /opt/suphp/bin/suphp