Unfortunately you'll have to keep using cs4 and earlier versions of our extensions in order to continue with Classic ASP. We announced dropping ASP classic more than a year ago now. You can still use the extensions, you just have to use the old version of the extension on the old version of DW that they supported, in this case CS4.
Eventually all of our extensions will stop working for Classic ASP and Coldfusion, and we won't support newer versions of Dreamweaver for those extensions after that point. Really you'll have to stop upgrading webassist extensions for anything other than dot releases since full version updates will drop Classic ASP.