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 ('2c27aafd6b42215d20cf31ba6f094b2c', -1, 1406079505, 1406079505, '36c56c7c', 0, 0, 0)

Line : 373
File : sessions.php