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 ('716f6bc4b5ba8b66b1aad0fa05072ce7', -1, 1472086545, 1472086545, '36a694fc', -1, 0, 0)

Line : 187
File : sessions.php