phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('c504e92ed20069798f86e4f1f465cac4', -1, 1461917177, 1461917177, '36e313c3', 0, 0, 0)

Line : 187
File : sessions.php