Quit xcode and simulator. Open organizer and click on Upload again. This worked for me.
I tried adding the account again and also reconnected the wifi but it did not work for me but quitting xcode did.
I had same issue, and I resolved it.
I got hint from @jab11
I have external storage for TimeMachine. Around a week ago TimeMachine start to fail backup my disk.
I plugged out external storage not properly When it happens.
So, try like below.
I hope this help.
I know that is late for answer but maybe my solution could help others.
Step 1: Go to Xcode --> preferences --> accounts
Step 2: Select your team name and click in view details
Step 3: Click in
Final step: Go to Window --> Organizer and try to upload again your app :D
Actually I think it is an issue at Apples server.
I just got through once 30 minutes ago but had set the wrong build version and now I get the same error again. I think we have to wait.
For me, I removed all accounts in XCode -> Preference -> Accounts and ADD account again, then it's working well.
I noticed that I had some connection problems. The ethernet cable was not fully plugged in. On wifi, make sure you have a good signal.