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 ('9536d9f6d363bbab1f7b0f398a1dc2bf', -1, 1462498932, 1462498932, '365b9d97', -1, 0, 0)

Line : 187
File : sessions.php