I was having that problem at first as well. Not sure if you are trying to launch from an icon on your desktop or not. I was (trying to launch from icon) and updater would come up, go through the motions, say starting client, and...nothing.
What I did was use the link at the beginning of Ender's thread to launch Ender's, logged in to a character, logged out and closed it completely. After that I was able to launch from my icon again. Hope it works for you.
Being powerful is like being a lady. If you have to tell people you are, you aren't. ~Margaret Thatcher