ScriptResource.axd 404 not found

I just ran into it with our server on IIS 6. It was handled by making sure to have in the system.web section (different for IIS7).

<httpHandlers>
  <remove verb="*" path="*.asmx"/>
  <add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
  <add verb="GET" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler" validate="false"/>
</httpHandlers>

I also saw this behavior on a hosted web service; the local version had no problem. After trying dozens of variation of system.web/httpHandlers and system.webServer/handlers statements, I finally gave up and tried the most inelegant solution of creating a dummy ScriptResource.axd - voila, it worked! I'm guessing there was some hidden validation setting in IIS at the hosting level despite setting 'validate=false' in web.config.

I had correct settings in web.config, I fixed the issue by changing the IIS 8 to run in 'Classic' mode rather than 'Integrated' mode.