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 ('bfe1f46b5ce93d6b7c1cf0d6fdf1b9c8', -1, 1432791864, 1432791864, '36a7b912', -1, 0, 0)

Line : 187
File : sessions.php