phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('32a08f32a847181f8b02544e486a9121', -1, 1406791414, 1406791414, '36e33fc3', 15, 0, 0)

Line : 180
File : sessions.php