Which version of the extension are you installing? Also did you have a previous version of the extension installed? If you do, try uninstalling that version before installing the latest version.
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.