What version of Application Loader do you have installed?
I'm using 3.0, downloaded from iTunes Connect.
You need the newest version of Application Loader. You can get it by downloading the most recent version of Xcode.
Thank you SO much!
It's weird, that Apple would leave old software on their iTunes Connect site. If you take a look, the download for the standalone Application Loader is for version 3.0.
I obviously took that, instead of Xcode, because I develop and test in another system, so there's not much need for the whole Xcode suite.
But I was wrong!