In older implementations (glibc), a group cannot have more than 200 members. The maximum line length of /etc/group is 1024 characters. Longer lines will be skipped. This limitation disappeared in newer version of glibc. Older binaries that are statically linked, depend on old shared libraries, may still have this limit.
More info can be found at The GNU C Library docs : http://www.gnu.org/software/libc/man...ode/index.html