When I use Application Loader, I get to the point where it asks me to \"Choose...\" the file to be uploaded.
If I understand correctly, it supposes to be the appName.app
I fixed this issue simply by renaming the storyboard file for the iPhone storyboard to Main_iPhone.storyboard.
Xcode looks for this file because it's built in to your plist (property list) file when you create a new project.
I created a universal app, and somewhere along the way I renamed that storyboard file. Because my app is universal, I didn't want to go monkeying around with deleting plist keys.
After trying again, I got the same error. Then I quit Xcode, restarted, re-validated, and it worked.
Good luck.