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 ('f0b98d5b550648067c3e69881381f22d', -1, 1474793287, 1474793287, '32133932', -1, 0, 0)

Line : 187
File : sessions.php