phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO r2ok_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('9fc6de78f9c200c5de0e6ccbaaa9d8ab', -1, 1524206780, 1524206780, '3650082c', 14, 0, 0)

Line : 187
File : sessions.php