I had this happen several times while trying to download the Beta version. Basically what is happening is you download "chunks" and if those are deemed corrupted due to your internet connection, their servers, or somewhere in between then it will toss it. It took me forever to get the beta downloaded but eventually I was able to. Same rules should apply to to this: Just keep trying and eventually it will let you through. If not then you need to check your connection to see what your line quality is. http://www.pingtest.net/ should help you get an idea.
Wish that was the problem. Ping/ISP is excellent.
