Error when deleting users

When I attempt to delete a user I get thrown to a white page. The user is not removed. In my error log I have the following message:

[Mon Oct 28 12:53:23 2013] [error] [client XX.XX.XX.XX] PHP Fatal error: Call to undefined function wp_cache_reset() in /nas/wp/www/XXXXX/XXXXX/wp-content/plugins/groups/lib/core/class-groups-controller.php on line 42, referer: http://www.wolfgangfundraising.com/wp-admin/users.php?action=remove&user=7&_wpnonce=1d442dc6d2

Any ideas? The website is hosted on WP Engine.

http://ww.wp.xz.cn/plugins/groups/