this function is found in moodle 1.8, but it not work in 2.0.
who knows which funtion is replaced for function get_group_students ?
please help me.
I'm not familiar with exactly what get_group_students did back in 1.8, however all group-related functions can now be found in lib/grouplib.php, so you can look through there and see if something like 'groups_get_members' covers your needs.