Before renaming the configuration folder, try a couple of tests to determine if it is necessary:
1) Uninstall Universal Email form the Extension Manager and install the latest version that is available from the download center. After reinstalling, delete the cache file again before opening Dreamweaver to see if the error persists when trying to edit that file.
2) Create a new page and add only Universal Email to it with a very simple message body. Save the page, close Dreamweaver and open it again and try to edit the Universal Email server behavior on that page to see if the error is specific to the page or a problem with the install.
