I have run into this issue 3 times where it stalls and does not do anything, each time I either hit the back button on the browser or just refreshed the page and it continued on its merry way without incident and everything was fine.
I think there is a browser issue involved here most of the time between the server and your computer. I have came to this reason for the fact that I'm litterly sitting right on top of the server while doing the upgrades and there is not internet or network issues. The server rack is like 8 feet from my desk.
