Here's an interesting one from yubeie in our Chromecast forums:
The Chromecast was successfully purchased and installed, but it wouldn't connect to the Wifi network. The culprit, it seems, was yubeie's 128-freakin'-character password. (A bit of which you can see here.) "Could not communicate with your Chromecast" was all the error message read.
That's ... quite the password. (Especially since WPA2 maxes out at 63 characters, but the point still stands here.) The good news is that changing it to something slightly less ridiculously robust seemed to do the trick.
So let that be a lesson to you, boys and girls. Chromecast doesn't like long-ass passwords.