Unexpected response from the backend server. The data received is invalid or in an unexpected format.
Oops, something serious went wrong. This is not expected to happen even in the usual error conditions and most likely means that either this site or the backend server of the game itself is broken.
Please let us know via the game forum and we'll take a look at it. Please include information about what you did that led to this error, and ideally the URL of this page.