Strange Errors on Archive Validation
I had the same problem with Xcode 8.2 while submitting my application:
ITunesSoftwareServiceAuthenticationErrorDomain error 434.Solution: I switched to different network and it worked for me.
Had the exact same problem. I tried upgrading to Sierra which seemed to update bits of Xcode etc. The new error message was formatted differently, so I could not see the "434" 
(With 1 success in 15 attempts (I had to tweak a version number in a string in the app, so didn't choose to upload after that brief moment of joy), i just uploaded the archive anyway, and after 2 hours of processing, it was accepted. I will update when my new app version is live to verify this error can be safely ignored, at least in some cases (e.g. I checked all my graphics' color profiles, etc.).