I faced with this problem for the first time after I updated IS. Now I have version 1 (update 14).
The problem: I create a new prototype. In this prototype I create 1 screen with repeater. Then I saved all and run prototype. But IS display error: "Hmm... We can't load this prototype. If this keeps showing, you might want to try out with another browser (though all modern ones are supported) or check our user forums."
It's also repeats when I generate HTML prototype and run it in chrome.
BUT! Prototypes, created in previous versions, running without problems.