What was the error on activating?
Was eCart installed last by chance? with eCart / design Extender / Data Bridge, you should ensure that eCart is not the last extension installed.
I always install in this order:
but it doesn't necessarily have to be in that order, just as long as eCart is not the last one you install.
try uninstalling eCart and Design Extender, then Delete the Dreamweaver Cache file from the users configuration folder:
and reinstall eCart then design extender last