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 ('ad32d741234548b9e32156c045b9c134', -1, 1414825934, 1414825934, 'ae815c7f', -1, 0, 0)

Line : 187
File : sessions.php