phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO forum_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('9cccd48683b1a5aecba217a2ab533f43', -1, 1540057980, 1540057980, '36e0387e', -6, 0, 0)

Line : 187
File : sessions.php