Since the Apple "Users & Roles" update to iTunesConnect end of november 2015 some people have been experiencing an error message "iTunes Store operation Failed" and "You are not authorized to use this service".
This happens when using XCode 6 and 7
Previously i was able to upload app using the same iTunes account.
I had the same issue today. What I did is mentioned below.
Go to XCode -> Preferences -> Accounts -> Apple Ids
From that select your Apple ID, remove it, and then add it again. Quit Xcode, open it again, and then clean and archive the project.
It worked for me.
Hope it works for someone else also.
EDIT
If your Apple ID is already there you can also try with refresh button for all provisioning profiles and certificates.
Then restart Xcode, clean and build the project. You'll be good to go!