Why do I get "setgid: Invalid argument" at startup?

Your Group directive (probably in conf/httpd.conf) needs to name a group that actually exists in the /etc/group file (or your system's equivalent). This problem is also frequently seen when a negative number is used in the Group directive (e.g., "Group #-1"). Using a group name -- not group number -- found in your system's group database (/etc/group) should solve this problem in all cases.