Watch these two videos. As far as for me (not a pro but a real hobbyist), they did the trick. Before following the recipes, I opened KEYCHAIN and deleted any profile having to do with iOs signing and installing. After having "a clean keychain", I managed to execute a Certificate Signing Request and to set up the App ID & Provisioning Profiles. Make also sure you've got the correct xcode-version going with your LC version (you can look this information up on LC site).