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 ('068e75a2035b796567f07a8f6663dd4b', -1, 1441003354, 1441003354, '3213873d', -1, 0, 0)

Line : 187
File : sessions.php