Invalid bundle structure - The app may contain only one executable file.

This question is similar if not identical but there is no solution. I've looked inside the archive and there's only one executable, so I am at a loss as to how to proceed. Any ideas greatly appreciates.

In hindsight the error is straightforward. An executable file was accidentally added to the project. In my case "Develop!.app/Xcode" meant that Xcode was the executable. Checking the list of files in the project I found a symlink to Xcode. (Maybe I dragged it from the dock somehow and dropped it into the project).

If you are getting this error look at the files in your project -- there is an executable there somewhere.