Just an FYI – this is happening to me, also. It has been impossible to upload videos to YouTube the past couple of days. Actually, I can upload short videos, say 30 seconds long – YouTube gives an error but processes the video anyway. Longer videos, such as 5 minutes, always fail. I suspect this is due to YouTube’s new 1080p upgrade not working.
Nothing changed on my end – or for the many others experiencing this problem. Today is Saturday, November 21, 2009 for reference.
There is a work around, apparently: Use the multi-video or bulk video upload option. This does work for me and others.