HTTP Error 404.3 - Not Found The page you are requesting cannot be served because of the extension configuration. If the page is a script, add

I found this error while deploying webservice  (.asmx) ,for this i found a solution you just need to do following steps :
Open Control Panel and click turn feature on  as shown in picture

go to Internet Information Services iis expend it then expend World wide web services  then

Application development Feature and check .Net Extensible ,Asp.net ISAPI Extension ISPAI Filters

press ok  now refresh you page it should work now :)