What is your OS?
What version of Dreamweaver are you using?
What version of eCart is installed?
What other extensions including the version numbers are installed?
have you tried:
reset the workspace layout:
go to Window -> Work Space layout -> Reset '<your layout name>'
Then close Dreamweaver and Delete the Dreamweaver Cache file from the users configuration folder:
http://www.webassist.com/tutorials/Common-installation-issues