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 ('c93b97f6d5444ca6afc5c43f9e97ec9c', -1, 1467360226, 1467360226, '36c655c4', 0, 0, 0)

Line : 201
File : sessions.php