Is Xcode 7b3 not codesigning your embedded binaries? Have you recently integrated a framework or similar that required you to turn off Bitcode? Well, get ready to remove that framework and turn Bitcode back on, because that's the cause of your codesigning issues.
If you have turned off Bitcode in your main app while leaving it on for your Watch app or similar, Xcode will throw a cryptic codesigning issue at you and leave you to figure it out (related). All you have to do to fix this is turn Bitcode back on. Of course, this means you will have to remove whatever thing you turned Bitcode off for.