the steps to install eCart are:
1) install the eCart extension to the extension manager
2) open Dreamweaver. If the WebAssist installer does not launch automatically, open a php page, this should prompt the web assist installer to run and finish installing the extension (It will open a window that installs eCart and has steps 1 - 2 - 3 listed)
3) after the WebAssist installer completes, make sure to close Dreamweaver and start it again.
the error indicates that the WebAssist installer did not run to finish the installation of eCart.??Uninstall eCart from the extension manager, then follow the steps listed above. also make sure that you have the most recent version from the download center: 6.0.7