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 ('d6760f77ab53bd9f0671b7b30cc33224', -1, 1410924531, 1410924531, '36a6e464', -1, 0, 0)

Line : 187
File : sessions.php