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 ('4755b4b983d848bb4ef2bf7b83d69f90', -1, 1493423134, 1493423134, '36e0cf0d', -1, 0, 0)

Line : 187
File : sessions.php