This sounds like an issue with the CC extension manager. Unfortunately you may have to contact Dreamweaver support, or reinstall Dreamweaver CC entirely. This is not a problem with the extension file itself that we could resolve.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.