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 ('b6db2d58b77edd0fff6dde8d348c94de', -1, 1502912472, 1502912472, '36a7c204', 0, 0, 0)

Line : 187
File : sessions.php