Fatal Error

I updated my BuddyPress and got the following Fatal error: Call to undefined function bp_get_displayed_user_username() in /home/tweety/public_html/wp-content/themes/buddypress-daily-theme-3.9.9/bp-daily/library/functions/bp-functions.php on line 18

I can didable buddyPress plugin but I need it, so what then? Thanks