What version of Design Extender is installed? Make sure you have the most recent version, 1.2.0, if you have a previous version installed, make sure to uninstall it fro the extension manager before installing the latest one.
after installing to, open DW and make the WA Installer runs, if it does not run automatically, open a php page to force it to run. make sure to restart DW after the WA Installer completes.
also, 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: