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 ('d1a0d65a5f91492fb30c75cc82587b39', -1, 1508343587, 1508343587, '36c421f6', 5, 0, 0)

Line : 187
File : sessions.php