Trivia corner: I got the same dialog box without changing account or IP address. It turned out that the App Store wants to use the Spotlight index (!) for some

Trivia corner: I got the same dialog box without changing account or IP address. It turned out that the App Store wants to use the Spotlight index (!) for some reason, and that "Fix permissions" somehow botched it. "sudo mdutil -i on -E /" fixed the issue. Let's just hope that nobody thinks about copying this insanely awesome design.