400. That’s an error.

Google cannot redirect you to http://worldcat.org/search?q=Bullarii+romani+continuatio+summorum+pontificum+Clementis+XIII,+Clementis+XIV,+Pii+VI,+Pii+VII,+Leonis+XII,+Pii+VIII+[et+Gregorii+XVI]:+Pii+VII.+Annum+quartum+ad+sextum+(1846.+XXI,+450+p.)+andreas+barberi+alexandre+spetia+(count) because the request was invalid.

This might be because the link was created a long time ago. Try your search again on Google. That’s all we know.