Data Assist hasn't been updated to work with MySQLi yet. We will be adding that in the next major update. For now you need to use a standard MySQL connection to work with Data Assist.
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.