Justin did a hot fix build for eCart a couple days ago.
Uninstall eCart from the extension manager, then install it again.
Make sure that the WebAssist Installer runs when you open DW, if it does not launch automaticly, open a php page to force it to launch.
after the WebAssist installer completes, make sure to restart the computer.
you may also need to Delete the Dreamweaver Cache file from the users configuration folder: