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 ('8446437cca7dddcd01cc1ee7f60ee86a', -1, 1469612034, 1469612034, '17144fe3', -1, 0, 0)

Line : 187
File : sessions.php