HTTP Error 500.23 after adding dotless to my local website

Question

Hi I'm trying to run dotless on my local .net4 web site

My web config looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="dotless" type="dotless.Core.configuration.DotlessConfigurationSectionHandler, dotless.Core" />
  </configSections>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
  <httpHandlers><add path="*.less" verb="GET" type="dotless.Core.LessCssHttpHandler, dotless.Core" /></httpHandlers></system.web>
<dotless minifyCss="false" cache="true" web="false" />

    <system.webServer>
        <handlers>
            <add name="dotless" path="*.less" verb="GET" type="dotless.Core.LessCssHttpHandler,dotless.Core" resourceType="File" preCondition="" />
        </handlers>
    </system.webServer>
</configuration>

Here is the error I get

HTTP Error 500.23 - Internal Server Error
An ASP.NET setting has been detected that does not apply in Integrated managed pipeline mode.
Most likely causes:

    This application defines configuration in the system.web/httpHandlers section.

Can you please help?

Answer 1

adding <validation validateIntegratedModeConfiguration="false"/> worked

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="dotless" type="dotless.Core.configuration.DotlessConfigurationSectionHandler, dotless.Core" />
  </configSections>
  <system.web>
    <compilation debug="true" targetFramework="4.0" />
  <httpHandlers>
      <add path="*.less" verb="GET" type="dotless.Core.LessCssHttpHandler, dotless.Core" />
  </httpHandlers>
  </system.web>
<dotless minifyCss="false" cache="true" web="false" />

    <system.webServer>
        <validation validateIntegratedModeConfiguration="false"/>
        <handlers>
            <add name="dotless" path="*.less" verb="GET" type="dotless.Core.LessCssHttpHandler,dotless.Core" resourceType="File" preCondition="" />
        </handlers>
    </system.webServer>
</configuration>

Answer 2

<validation validateIntegratedModeConfiguration="false"/> tells IIS to ignore configuration issues. One such issue seems to be the fact that dotless automatically adds a handler to system.web and system.webServer. The former section is used by the classic application pool mode, whereas the latter by the new integrated application pool mode. Since I am using the integrated mode, removing the handler in system.web helped just as well.