Cocoa: Command /usr/bin/ditto failed with exit code 1

clean your project and see whether it help or not

Command + Shift+ K

or

Product > Clean

Or check this link it may helps you: http://codica.pl/2015/12/25/taming-swift-compiler-bugs/

For Mac OS Sierra, this work for me:

cd /Users/YOUR_USER_NAME/Library/Developer/Xcode/DerivedData

then

xattr -dr com.apple.FinderInfo *

and then rebuild your project..

and fix the error!

All of sudden, It happens to my Mac app project today in Xcode 7.3.1.

What I did : Clean >Clean build folder > Quit Xcode >Open Finder then go to

~/Library/Developer/Xcode/DerivedData

then deleated everything inside >Open Xcode >Build >Run

I think this is happening when something is wrong adding a file into Xcode. I have not encountered since readding myApp.help file without the option 'Destination: Copy items if needed'.