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 ('ec44392cc51d77d7b4400a2ddc2b714b', -1, 1416650764, 1416650764, '36a790ca', -4, 0, 0)

Line : 187
File : sessions.php