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) VALUES ('53f8a52de1e280279bacf98faafb1dd6', -1, 1409676245, 1409676245, '36a6111a', 2, 0)

Line : 158
File : /forum/includes/sessions.php