MapRequestHandler issue in IIS for .net websites

I found I'd gotten this same error after making a few changes to the site configuration of my applicationhost.config file. After looking more closely and comparing some sites which were working correctly against other sites which weren't working correctly, I noticed that I had apparently whacked the parent application configuration for a few of my sites.

Here's an example of the site configuration when I was getting the "Unrecognized configuration path" 500.19 error:

<site name="Peanuts-Site" id="2345">
    <application path="/peanuts" applicationPool="Clr4IntegratedAppPool">
        <virtualDirectory path="/" physicalPath="C:\websites\Peanuts" />
    </application>
    <bindings>
        <binding protocol="http" bindingInformation="*:80:localhost" />
    </bindings>
</site>

And here's what it looked like after I restored the deleted parent application:

<site name="Peanuts-Site" id="2345">
    <application path="/" applicationPool="Clr4IntegratedAppPool">
        <virtualDirectory path="/" physicalPath="C:\Users\firstname.lastname\Documents\My Web Sites\Peanuts-Site" />
    </application>
    <application path="/peanuts" applicationPool="Clr4IntegratedAppPool">
        <virtualDirectory path="/" physicalPath="C:\websites\Peanuts" />
    </application>
    <bindings>
        <binding protocol="http" bindingInformation="*:80:localhost" />
    </bindings>
</site>

Unbeknownst to me at the time, IIS Express seems to require a an application to be defined that's mapped to the site root when specifying any application not mapped to the site root. And on second thought, this requirement actually does make sense after all.

Lesson learned -- Don't go on an overzealous pruning spree unless you know what you're doing. I'm just glad I remembered what I did so I could fix it later.

Just found that lines below must be added to web.config file, now everything works fine on production server too.

<system.webServer>
  <modules runAllManagedModulesForAllRequests="true" >
   <remove name="UrlRoutingModule"/>    
  </modules>
</system.webServer>