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 ('ca24e7f14e02dc29f5f1606697c0bee4', -1, 1422231555, 1422231555, '36a78a35', 7, 0, 0)

Line : 189
File : sessions.php