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 ('ad0651e8a5c5b6855d608504af5ef424', -1, 1472080186, 1472080186, '17148149', -1, 0, 0)

Line : 187
File : sessions.php