mono/mcs/class/System.Web.Services/Test/standalone/server/web.config

<configuration>
  <system.web>
     <httpHandlers>
       <add verb="*" path="*.vsdisco"
           type="System.Web.Services.Discovery.DiscoveryRequestHandler, System.Web.Services" validate="false"/>
     </httpHandlers>
   </system.web>
</configuration>