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 ('590b3df69a5ca42a0a04409f3a62649a', -1, 1409640256, 1409640256, '36c48877', 13, 0)

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