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, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" validate="false"/>
     </httpHandlers>
   </system.web>
</configuration>