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 ('8e49a45295b520b877cc2520d5d4f9b1', -1, 1406365622, 1406365622, '36c4c46c', 37, 0, 0)

Line : 180
File : sessions.php