I was experiencing the exact same error hence being here (failed about 6 times over an hour).
I just tried again now (without changing anything), it worked by itself.
I read on the Apple-forums that it's an issue with Apple servers, nothing to do with your Xcode.
I also read that others trying the upload via ApplicationLoader (Menu -> Xcode -> Open Developer Tool -> Application Loader), this will ask where your code is, you would then have to select your Archive (not the source code), you can upload your code this way if you need. I personally prefer the built-in Xcode instead.
Works either way.
For the record, I am copying the thread from Apple Forums.
Cheers Heider