I have a fresh install of Moodle 2.1 and get the following error when I try to view an overview report of a quiz with group mode turned on:

Fatal error: Call to undefined function get_in_or_equal() in /var/www/moodle_21/moodle/mod/quiz/report/overview/report.php on line 512

All other calls to this function within the quiz_overview_report class call this function using $DB->get_in_or_equal() so this could be a typo.

By changing line 512 to read:

list($usql, $params) = $DB->get_in_or_equal($groupstudents);

The error does not occur and the report is visible. However, with full debugging turned on, there are other non-fatal errors, namely:

Warning: Missing argument 3 for quiz_report_feedback_for_grade(), called in /var/www/moodle_21/moodle/mod/quiz/report/overview/overview_table.php on line 78 and defined in /var/www/moodle_21/moodle/mod/quiz/report/reportlib.php on line 259

Notice: Undefined variable: context in /var/www/moodle_21/moodle/mod/quiz/report/reportlib.php on line 285

Notice: Trying to get property of non-object in /var/www/moodle_21/moodle/mod/quiz/report/reportlib.php on line 285

I don't know what the policy is regarding non-fatal errors in core Moodle activities, but the first bug should be corrected ASAP.