Site Assist is not compatible with Dreamweaver CC.
You will need to upgrade to Design Extender to use Site Assist in DW CC.
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.