This should have been fixed in the latest hot fix released a couple days ago, Try uninstalling Design Extender and reinstalling it, make sure the WA Installer runs when you open DW, and restart after it completes.
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.