phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '0' 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 ('c7a6696c445738f2e002e77fd398cb83', -1, 1550658764, 1550658764, '345bb0fb', -4, 0, 0)

Line : 187
File : sessions.php