[Solved] Could not load type 'System.ServiceModel.Activation.HttpModule'

For Windows 7 and Windows Server 2008, use the ASP.NET IIS Registration Tool (aspnet_regiis.exe,) to register the correct version of ASP.NET. For more information about the aspnet_regiis.exe, see ASP.NET IIS Registration Tool.

To register the correct version of ASP.NET

1. On the computer that is running Microsoft Dynamics NAV Web Server components, open a command prompt as an administrator as follows:
   1. From the Start menu, choose All Programs, and then choose Accessories.
   2. Right-click Command Prompt, and then choose Run as administrator.
2. At the command prompt, type the following command to change to the Microsoft.NET\Framework64\v4.0.30319 folder, and then press Enter.
   cd\Windows\Microsoft.NET\Framework64\v4.0.30319
   

3. At the command prompt, type the following command, and then press Enter.
   aspnet_regiis.exe -iru
   

4. At the command prompt, type the following command, and then press Enter.
   iisreset

Source: MSDN Library