make sure both Dreamweaver and the Extension Manager are closed, then try manually deleting the file:
C:\Users\Rich\AppData\Roaming\Adobe\Dreamweaver9\c onfiguration\Shared\WebAssist\CSSMenuWriter\preset s\Midnight\CaboSunset\menu_bg_l.jpg
After that, try uninstalling the extesnion in the extension manager again. If all else fails, try renaming the configuration folder at:
C:\Users\Rich\AppData\Roaming\Adobe\Dreamweaver9\configuration