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 ('3c0b10c8e0003b3956fd40b15e8ac559', -1, 1422368423, 1422368423, '36e3d78d', 0, 0, 0)

Line : 189
File : sessions.php