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 ('b9b1fbf93f4082d7a4b6e4468ac94a4d', -1, 1513306194, 1513306194, '365acf4b', 6, 0, 0)

Line : 189
File : sessions.php