CFBundleVersion must be higher than previous version
FYI. Apple thinks 1.11 > 1.2, so if you are going from 1.11 to 1.2 you need to go all the way to 1.20.
Enjoy.
It turns out that I had some problem in my original submission which caused the user-visible version to be "1.0" but the internal bundle version to be "1.2". So I changed my new version to be 1.3 and 1.3 and the submission worked.
Same thing happened to me. My current App Store version was 2.03. I attempted to upload 2.1. All I had to do was change it to 2.10 and it worked.
Increasing the CFBundleShortVersionString or "Bundle versions string, short" did the Job for me.