If I remember correctly, your connection wasn't too quick? Youtube is pretty rubbish on slow connections, sometimes just dropping the video halfway through, so yours might be an extreme version of that. I use a couple of internet connections and when I use iBurst (1MB/s) I get sad whenever there's a link to youtube. I think they've been 'optimizing' algorithms to save costs, and the result is a flakier video stream than before.
Backup method is this: 1) Google "download youtube video" and use whichever solution you prefer. An obvious candidate is downloadyoutubevideo.org 2) You'll get a download link from them, which you can then download normally. 3) If the connect issues persist through normal download, use http://www.freedownloadmanager.org/ to download the file. It'll generally always be able to download via a flaky connection, even if it has to claw every byte down from the internet using its bare hands. To download a file from a url, right-click the url and say "copy" (or similar), and then start free download manager and click the "+" to add a new download.