make sure you are downloading the latest ZXP Extension versions of eCart 5, Data Bridge, Design Extender, and Free Tools from the download section of your account.
Also, make sure to install the Deprecated Server Behaviors extension:
http://www.webassist.com/tutorials/Server-behaviors-for-Dreamweaver-Creative-Cloud
if you continue to have problems, please provide more details such as the text of the error message. It is impossible to know the cause of an error without knowing what the error says.