Whenever I try to use the Google login button, I get that^^. Seems like it never navigates away from the site (it happens both when I'm logged in and logged out of Google). Strangely, if I put the Google OpenId endpoint link in the "other" box and log in, it works.
Today morning (from mobile), I had the same problem with the SE login as well. Fortunately my cookies had me logged in on Chem.SE, and I could add the Google login (which had mysteriously disappeared from "my logins", though now my user history shows no sign of me adding it again this morning)
Seems like a bug to me.