During an automated install/deinstall check the following error has happened:

ERROR: Output running post uninstall script for package rpm-0:4.4.2-39.fc7.i386
groupdel: group rpm does not exist

Redirecting the userdel and groupdel commands to /dev/null fixes the problem.

postuninstall scriptlet (using /bin/sh):
if [ $1 = 0 ]; then
    /usr/sbin/userdel rpm > /dev/null 2>&1
    /usr/sbin/groupdel rpm > /dev/null 2>&1
fi
exit 0