pngcrush caught libpng error: Not a PNG file..

While reading /XXX/XXX/XXX/img1.png pngcrush caught libpng error:  Not a PNG filCould not find file:/Users/XXX/Library/Developer/Xcode/DerivedData/CookBookDemo-cnttcobrbmvbddeiesgsxnfwihfe/Build/Products/Debug-iphoneos/CookBookDemo.app/img1.pngCommand/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/copypngemitted errors but did not return a nonzero exit code to indicatefailure