Solve IIS 8 Error: Could not load type ‘System.ServiceModel.Activation.HttpModule’

Introduction

I encountered an error when I was deploying my WebSocket server application which targeted .NET 4.5 to Windows Server 2012 plus IIS 8. It was an exception shown in browser whenever I tried to open a web page. The exception said:

"Could not load type ‘System.ServiceModel.Activation.HttpModule’ from assembly
 'System.ServiceModel, Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'"

When I was working on IIS 7.5, I heard about this problem and knew the cause: the default configuration in applicationHost.config (in C:\Windows\System32\inetsrv\config) declared two conflicted modules and two conflicted handlers:

<modules>
  <add name="ServiceModel" type="System.ServiceModel.Activation.HttpModule, 
  System.ServiceModel, Version=3.0.0.0, Culture=neutral, 
  PublicKeyToken=b77a5c561934e089" preCondition="managedHandler" />
  <add name="ServiceModel-4.0" type="System.ServiceModel.Activation.ServiceHttpModule, 
  System.ServiceModel.Activation, Version=4.0.0.0, Culture=neutral, 
  PublicKeyToken=31bf3856ad364e35" preCondition="managedHandler,runtimeVersionv4.0" />
</modules>
<handlers>
  <add name="svc-Integrated" path="*.svc" verb="*" 
  type="System.ServiceModel.Activation.HttpHandler, System.ServiceModel, Version=3.0.0.0, 
  Culture=neutral, PublicKeyToken=b77a5c561934e089" preCondition="integratedMode" />
  <add name="svc-Integrated-4.0" path="*.svc" verb="*" 
  type="System.ServiceModel.Activation.ServiceHttpHandlerFactory, 
  System.ServiceModel.Activation, Version=4.0.0.0, Culture=neutral, 
  PublicKeyToken=31bf3856ad364e35" preCondition="integratedMode,runtimeVersionv4.0" />
</handlers>

As we know, applicationHost.config contains the root settings for all web sites and web applications on the server. Therefore, any web application would have all the four conflicted modules and handlers loaded by default. “ServiceModel” and “svc-Integrated” were for .NET Activation 3.x while “ServiceModel-4.0” and “svc-Integrated-4.0” were for .NET Activation 4.x. Unfortunately, the 3.x items were declared before the 4.x items. That was why the exception occurred for a .NET 4.x web application!

Then how did such a situation happen? On Windows Server 2008, it could happen when you install .NET 3.x framework or IIS 7.5 with Activation features after .NET framework 4.x is installed. However, on Windows Server 2012, it always happens when you install .NET framework 3.x with Activation features.

Microsoft officially announced the solution (http://support.microsoft.com/kb/2015129) for Windows Server 2008 plus IIS 7.5: manually running “aspnet_regiis.exe /iru” for .NET framework 4.x (in C:\Windows\Microsoft.NET\Framework\v4.0.30319 or C:\Windows\Microsoft.NET\Framework64\v4.0.30319). However, aspnet_regiis.exe is not allowed to run for IIS 8. I tried manually changing applicationHost.config. I also tried removing and adding features in a good order. But all these solutions did not work.

The final solution was to delete the 3.x module and handler from IIS manager. You could delete them at the application or site level if you want to keep them in applicationHost.config. But I wanted to delete them from applicationHost.config. So I did the following steps:

1. In IIS manager, click the machine name node.
2. In “Features View”, double-click “Modules”.
3. Find “ServiceModel” and remove it.

   

4. Go back to the machine name node’s “Features View”, double-click “Handler Mappings”.
5. Find “svc-Integrated” and remove it.

   

Now everything works well.

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