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 ('7e5fa1b7d4db0eba4429b1a19b2fe02b', -1, 1462457849, 1462457849, '365aa048', -1, 0, 0)

Line : 187
File : sessions.php