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 ('f3687e5072d9264cc20e08932b07401f', -1, 1472303921, 1472303921, '365c9b4d', -1, 0, 0)

Line : 187
File : sessions.php