If you have trouble with an out of date client, try the following: in your browser address bar type: http://live.cardhunter.com/index.htm?v=325498534 where the numbers after "v=" are some nonsense. This will force it to fetch a new version of the client. We're working on making sure this isn't necessary, but it's a work-around for now.
You will tend to get an out of date client for up to 10 minutes after a new build is deployed. This is while Amazon propagates the new files out through its could front network. The answer is to wait a few minutes.