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 ('8bd22acd7cce8e50763c733611eb05b1', -1, 1418949113, 1418949113, '36a1b9f4', 1, 0, 0)

Line : 226
File : sessions.php