locate the users configuration folder, see this page for details:
http://www.webassist.com/tutorials/Common-installation-issues
rename the configuration folder, then restart DW to recreate it.
now close dw, and open the extension manager. in the extension manager, remove the extension then reinstall them.
after installing them, when you open DW, it should launch the WebAssist installer to complete the installation. make sure to restart DW after the WebAssist installer completes.