Hmm. Not sure. What browser and version of Flash are you using? When is the last time you updated Flash? You need at least version 8 for most of our templates. Do you have any antivirus software running? Do you get the hangups for all browsers? Has it ever not hung for you? Does it work fine when previewing directly from myUdutu?
It's hard to tell what is at play, here. If you can supply answers to the above questions, it would help narrow the field.