I\'m not sure if I am the only one experiencing this program, but I have tried searching and have not been able to find anyone in my current situation. I downloaded Xcode 6
I had the same problem. The solution was to not try to add the extension in File/new/File... menu but in File/new/Target... menu.
File/new/File...
File/new/Target...
You can add extension to any existing project.
You create a extension by creating a new target in an existing project.
Check this link for more information