400. That’s an error.

Google cannot redirect you to http://worldcat.org/search?q=P.+Virgilii+Maronis+opera:+nunc+emendatiora+[ed.+C.+Grierson].+publius+vergilius+maro 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.