Unfortunately, this is a problem with the new extension manager, we will be looking into a long term fix, but for now, it is just a matter of being patient while the extensions install.
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.