XCode 5 code signing: cannot find code object on disk

I've upgraded to XCode 5 and want to sign a Mac App Store application. The signing worked fine in XCode 4, but something seems to have changed. When I run now the code signing like this:

codesign -f -v -s "Developer ID Application: Martin Schultz" "/Users/Martin/Development/Mac App Store/RC Mini Racers 2.5/Builds/RC Mini Racers.app/Contents/Frameworks/MonoEmbedRuntime/osx/libmono.0.dylib"

I get:

/Users/Martin/Development/Mac App Store/RC Mini Racers 2.5/Builds/RC Mini Racers.app/Contents/Frameworks/MonoEmbedRuntime/osx/libmono.0.dylib: cannot find code object on disk

Anyone knows a way to solve this? The path to the dylib is definitely correct.