What version of DW are you using? that is the folder you should be looking in, the one that matches the version of DW you are using.
try uninstalling the MySQLi extension from the extension manager, then reinstalling it.
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.