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 ('ed536c35fb30c68e784da3243c3d4e4c', -1, 1435878391, 1435878391, '36509935', -1, 0, 0)

Line : 187
File : sessions.php