You don't say what OS you're using but the method that works for me is:
- Make sure that DW is closed.
- Remove the old version of the extension. (critical).
- Download the latest version if necessary (never assume what you downloaded last week is the latest).
- Check for known issues in your download area.
- Install new extension.
- Click "Yes to all" for duplicates.
- Clear the cache to make sure DW creates a new one for the new extension.
- Start DW and activate the new extension.
- Repeat starting at 1 for each new extension.
I try to install eCart after the other extensions.
There is more information here:
Solving problems with Dreamweaver
Sounds like you should delete the config folder to be safe.
If you can't get it resolved here, someone from WA will open a ticket for you when they get back from the weekend. You can clear your activations in you account area if that becomes necessary.