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 ('549a08abc9b60bc2dc6e4f07a9bd4e93', -1, 1409657345, 1409657345, '36c52ace', -1, 0, 0)

Line : 187
File : sessions.php