HTTP Error 500.19 - Internal Server Error - system.webServer/httpErrors is missing a section declaration

I have the following:

  <system.web>
    <compilation debug="true" targetFramework="4.5"/>
    <httpRuntime targetFramework="4.5"/>
    <customErrors mode="Off"/>   </system.web>

and also:

<system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit"/>
      <remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit"/>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0"/>
      <remove name="OPTIONSVerbHandler"/>
      <remove name="TRACEVerbHandler"/>
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness32" responseBufferLimit="0"/>
      <add name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" modules="IsapiModule" scriptProcessor="%windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll" preCondition="classicMode,runtimeVersionv4.0,bitness64" responseBufferLimit="0"/>
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="GET,HEAD,POST,DEBUG,PUT,DELETE,PATCH,OPTIONS" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0"/>
    </handlers>
  </system.webServer>

When I run my application I am getting an error page saying:

HTTP Error 500.19 - Internal Server Error
The requested page cannot be accessed because the related configuration data for the page is invalid.

Detailed Error Information:
Module     CustomErrorModule
Notification       SendResponse
Handler    Not yet determined
Error Code     0x80070490
Config Error       The configuration section 'system.webServer/httpErrors' cannot be read because it is missing a section declaration

Can someone help explain this for me.

I thought with the that I didn't need to have a custom error page. However everything I read tells me that the solution is to add a custom error page.

In hope that the following answer will help someone later on, I will share my experience with this issue.

This error can appear due to various reasons. Lately, I have experienced the error due to the following reasons:

• Missing URL Rewrite Module.

My Web.config file contains a <rewrite></rewrite> section which requires the IIS URL Rewrite Module to be installed (can be done using the Web Platform Installer).

• Upgrade of Azure SDK.

My Web.config file contained the following entry:

<system.diagnostics>
  <sharedListeners>
    <add type="Microsoft.WindowsAzure.Diagnostics.DiagnosticMonitorTraceListener,
               Microsoft.WindowsAzure.Diagnostics,
               Version=2.3.0.0,
               Culture=...
               PublicKeyToken=...">

After upgrade of Azure SDK (2.3.x -> 2.6.x), this "hard" dependency on version 2.3.x could not be resolved. To resolve this, I removed the Version element entirely (including Culture and PublicKeyToken), since a dependency on the most recent assembly version is fine in my case.