I was too having this issues, I had uploaded my application and also updated it once but had no issues, but as i was uploading it for the 3rd time, i came across this issue, tried hell lot of things, scratched my head, googled it for hours, kept on trying the whole day, but nothing happened, but next day( a new light came) and my app uploaded on the first attempt.
Feel like there was some issue from apple side(be it there server, there software xCode or there mac).
So don not get dishearten if facing this problem, you can explore diff things with this problem but its just simple thing to correct this issue is to wait for some time take rest and try again.