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 ('5430d8a003d2b2178a9f804b2b891ff9', -1, 1462375847, 1462375847, '36535085', -1, 0, 0)

Line : 187
File : sessions.php