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 ('b4f32a114ef6e6de95c160c057c9f27b', -1, 1409701194, 1409701194, '6b14253e', 0, 0, 0)

Line : 373
File : sessions.php