400. That’s an error.

Google cannot redirect you to http://worldcat.org/search?q=Excellentissimi+artiu[m]+sacre+theologie+doctoris+d[omi]ni+Egidii+Romani+[...]+i[n]+libros+Posterio[rum]+Arist.+expositio+aegidius+romanus+(archbishop+bourges) 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.