What version of Dreamweaver are you using?
You may have to close Dreamweaver and delete your user's configuration folder. That will effectively uninstall all extensions and you should be able to reinstall any you need at that point.
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.