Calendar Export crashes if Option "all event" is choosen.

Error Message:
[Fri Jun 05 16:27:39 2009] [error] [client 141.89.70.106] PHP Fatal error: Call to undefined function groups_get_all_groups() in /opt/csw/apache2/share/moodle/moodle_test/calendar/export_execute.php on line 39

Indeed, in line 39 of export_execute this function is called:
    34 if ($what == 'all') {
    35 $users = $user->id;
    36 $groups = array();
    37 foreach ($courses as $course) {
    38 $course_groups = groups_get_all_groups($course->id, $user->id);
    39 if ($course_groups) {
    40 $groups = $groups + array_keys($course_groups);
    41 }
    42 }

but I could not find the place where this function is declared/defined.

Steps to reproduce:
- Choose a Calendar block.
- pick a month
- in the "detailed month view", click on "Export calendar".
- leave the "Export" option on "all events" and click "Export"
In my environment, a blank page occures and I found the error message in the lock.

The problem is not solved in 1.8.9.