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 ('07e07dd9a0fc931fb91a34489befd3b9', -1, 1461909771, 1461909771, '365a9d23', 14, 0, 0)

Line : 187
File : sessions.php