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 ('9c7eddd3523e6310e18e116f1bf868b8', -1, 1467366539, 1467366539, '369ed119', 0, 0, 0)

Line : 201
File : sessions.php