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 ('5984ce2e79d781c8e101bb9b27eff05a', -1, 1405350737, 1405350737, '36513278', 50, 0, 0)

Line : 180
File : sessions.php