The SharePoint web services found in /_vit_bin/ for services like lists.asmx can only be reached at the webs. So the url must be in the format http://siteurl/sites/sitecollectionurl/_vti_bin/lists.asmx
You should be able to drop that url format in the browser and see the wsdl. If you do not, then the url is not correctly formatted.
Maybe you should try to use the action "Web request" to call this url :
Hope this helps