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 ('14ff4ebbd13a2d27a93e3e3093049223', -1, 1464555890, 1464555890, '3691757f', -1, 0, 0)

Line : 187
File : sessions.php