400. That’s an error.

Google cannot redirect you to http://worldcat.org/search?q=Sancti Agobardi,... Opera quae octingentos annos tenebris delituerant, nunc e Papirii Massonis,... bibliotheca proferuntur. Accesserunt binae epistolae Leidradi, non antea excusae... agobard masson duval 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.