I ran across this issue with the beta version of eCart, but have not experienced in the release version.
Did you participoate in the eCart beta?
try and Deleting the Dreamweaver Cache file from the users configuration folder:
http://www.webassist.com/tutorials/Common-installation-issues
or rename the configuration folder to start from a clean installation.
http://helpx.adobe.com/dreamweaver/kb/troubleshoot-javascript-errors-dreamweaver-cs4.html#main_user_config