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 ('a6f2f2e30b2ba7360adfd0f49aad57a1', -1, 1539933960, 1539933960, '36a6cfdf', 9, 0, 0)

Line : 187
File : sessions.php