in my opinion this is 1 of 2 things, bad script in your scripts dir or bad client
try building a new client.
also make sure your scripts directory is clear besides core.js
Try doing what the above user said, but also make sure that you are running the client in a web browser, such as google chrome. Someone posted a video showing how to do so.
You do not need to be running your client in a browser.
This is worth a try but I have never had to do that.