That’s odd. All it does it call
File::startAsProcess() on the
DemoRunner.xcodeproj file. Are you able to open that file manually?
I got a solution from Fabian at email@example.com “If you are compiling the Projucer yourself, then you also first need to build the DemoRunner project in examples.”
I opened the example projucer for demo runner and build it in my IDE.