Try renaming the configuration folder with Dreamweaver and extension manager closed. The configuration folder is the one that contains the winfile cache. This will have the result of disabling all your extensions. Then open up Extension Manager and remove Site Import and install it again. Open Dreamweaver again and See if Site Import is working correctly. If it isn't shut down Dreamweaver and Extension manager, delete the current Configuration folder and rename the old one back to Configuration. If its working, then you will have to install the extensions again.