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 ('324b1d4d32bf6cdb70ecf5fea2952b56', -1, 1455278310, 1455278310, '365349c8', -1, 0, 0)

Line : 187
File : sessions.php