Mobocracy

This worked for me too. Physically disconnect your internet and wait a while, then restart your computer, reconnect your internet, and try again.

Same issue began for my friend and me just today. He's the original save owner, and he gets the error that Ody shared above: "CANNOT LOAD SHARED WORLD". I was the last person to host and I don't get this error, I just see "Processing" which circles forever, and all of the saves and backups are visible but clicking on "Load" does nothing.