I had submitted the application via Application Loader 3.1. It shows "invalid package Applications built with SDK 9.0 or later must be packaged as proper IPA files."
I had received an Email on Sep 12 from Apple which allow to submit apps built by Xcode 7 GM.
Ran into the same problem today. Turns out Application Loader 3.2 now requires the file to be .ipa only. It for some reason still accepts .zip files but will fail with this error. So just change the file extension to .ipa, assuming the contents were properly generated.