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 ('693321c89ff62cea3d8ec7b5f0f87e1e', -1, 1419150407, 1419150407, '36ed4ea5', 5, 0, 0)

Line : 189
File : sessions.php