[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to… web.config issue

I have a problem like this on server

[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.HostSection. Type A originates from ‘System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ in the context ‘Default’ at location ‘C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll’. Type B originates from ‘System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ in the context ‘Default’ at location ‘C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_1.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll’.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidCastException: [A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.HostSection. Type A originates from ‘System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ in the context ‘Default’ at location ‘C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll’. Type B originates from ‘System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ in the context ‘Default’ at location ‘C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_1.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll’.

Solution

1. Backup your project. This walkthrough will require you to make changes  to your project file, package configuration, and web.config files.
2. For upgrading from Web API to Web API 2, in global.asax, change:

   WebApiConfig.Register(GlobalConfiguration.Configuration);

   to

   GlobalConfiguration.Configure(WebApiConfig.Register);

3. Make sure all the packages that your projects use are compatible with  MVC 5 and Web API 2. The following table shows the MVC 4 and Web API related  packages than need to be changed. If you have a package that is dependent on  one of the packages listed below, please contact the publishers to get the  newer versions that are compatible with MVC 5 and Web API 2. If you have the  source code for those packages, you should recompile them with the new  assemblies of MVC 5 and Web API 2.

   Package Id	Old version	New version
   Microsoft.AspNet.Razor	2.0.x.x	3.0.0
   Microsoft.AspNet.WebPages	2.0.x.x	3.0.0
   Microsoft.AspNet.WebPages.WebData	2.0.x.x	3.0.0
   Microsoft.AspNet.WebPages.OAuth	2.0.x.x	3.0.0
   Microsoft.AspNet.Mvc	4.0.x.x	5.0.0
   Microsoft.AspNet.Mvc.Facebook	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.Core	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.SelfHost	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.Client	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.OData	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.WebHost	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.Tracing	4.0.x.x	5.0.0
   Microsoft.AspNet.WebApi.HelpPage	4.0.x.x	5.0.0
   Microsoft.Net.Http	2.0.x.	2.2.x.
   Microsoft.Data.OData	5.2.x	5.6.x
   System.Spatial	5.2.x	5.6.x
   Microsoft.Data.Edm	5.2.x	5.6.x
   Microsoft.AspNet.Mvc.FixedDisplayModes		Removed
   Microsoft.AspNet.WebPages.Administration		Removed
   Microsoft-Web-Helpers		Microsoft.AspNet.WebHelpers

   Note: Microsoft-Web-Helpers has been replaced  with Microsoft.AspNet.WebHelpers. You should remove the old package first,  and then install the newer package.

   There is no cross version  compatibility among major ASP.NET packages. For example, MVC 5 is compatible  with only Razor 3, and not Razor 2.

4. Open your project in Visual Studio 2013.
5. Remove any of the following ASP.NET NuGet packages that are installed.  You will remove these using the Package Manager Console (PMC). To open the  PMC, select the Tools menu and then select Library  Package Manager, then select Package Manager Console.  Your project might not include all of these.

   1. Microsoft.AspNet.WebPages.Administration
      This package is typically added when upgrading from MVC 3 to MVC 4.  To remove it, run the following command in the PMC:
      Uninstall-Package -Id Microsoft.AspNet.WebPages.Administration
   2. Microsoft-Web-Helpers
      This  package has been rebranded as Microsoft.AspNet.WebHelpers.  To remove it, run the following command in the PMC:
      Uninstall-Package -Id Microsoft-Web-Helpers
   3. Microsoft.AspNet.Mvc.FixedDisplayMode 
      This package contains a work around for a bug in MVC 4 that has been  fixed in MVC 5. To remove it, run the following command in the PMC:
      Uninstall-Package -Id Microsoft.AspNet.Mvc.FixedDisplayModes

6. Upgrade all the ASP.NET NuGet packages using the PMC. In the PMC, run  the following command:
   Update-Package
   The Update-Package command without any parameters will update every  package. You can update packages individually by using the ID argument. For  more information about the update command, run get-help update-package.

Update the Application web.config File

Be sure to make these changes in the app web.config file, not the web.config file in the Views folder.

Locate the <runtime>/<assemblyBinding> section, and  make the following changes:

1. In the elements with the name attribute “System.Web.Mvc”, change the  version number from “4.0.0.0” to “5.0.0.0”. (Two changes in that element.)
2. In elements with the name attribute “System.Web.Helpers” and  “System.Web.WebPages” change the version number from “2.0.0.0” to “3.0.0.0”.  Four changes will occur, two in each of the elements.

   <runtime>   <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">     <!--Two elements removed for Clarity -->     <dependentAssembly>       <assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" />       <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />     </dependentAssembly>     <dependentAssembly>       <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />       <bindingRedirect oldVersion="1.0.0.0-5.0.0.0" newVersion="5.0.0.0" />     </dependentAssembly>     <dependentAssembly>       <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" />       <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />     </dependentAssembly>     <!--WebGrease element removed for Clarity -->   </assemblyBinding

3. Locate the <appSettings> section and update the  webpages:version from 2.0.0.0.0 to 3.0.0.0 as shown below:

     <appSettings>     <add key="webpages:Version" value="3.0.0.0" />     <add key="webpages:Enabled" value="false" />     <add key="PreserveLoginUrl" value="true" />     <add key="ClientValidationEnabled" value="true" />     <add key="UnobtrusiveJavaScriptEnabled" value="true" />   </appSettings>

4. Remove any trust levels other than Full. For example:

     <securityPolicy>    <!--<trustLevel name="Medium"  policyFile="web_mediumtrust.config"/>-->
   </securityPolicy>

Update the web.config files under the Views folder

If your application is using areas, you will also need to update each web.config file in the Views sub-folder of each Area folder.

1. Update all elements that contain “System.Web.Mvc” from version “4.0.0.0”  to  version“5.0.0.0”.

   <system.web.webPages.razor>   <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />   <pages pageBaseType="System.Web.Mvc.WebViewPage">     <namespaces>       <add namespace="System.Web.Mvc" />       <!--Elements removed for Clarity.-->     </namespaces>   </pages>
   </system.web.webPages.razor>
   

     -->   <pages       validateRequest="false"       pageParserFilterType="System.Web.Mvc.ViewTypeParserFilter, System.Web.Mvc, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"       pageBaseType="System.Web.Mvc.ViewPage, System.Web.Mvc, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35"       userControlBaseType="System.Web.Mvc.ViewUserControl, System.Web.Mvc, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">     <controls>       <add assembly="System.Web.Mvc, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" namespace="System.Web.Mvc" tagPrefix="mvc" />     </controls>   </pages>
   </system.web>

2. Update all elements that contain “System.Web.WebPages.Razor”  from  version “2.0.0.0”  to  version“3.0.0.0”. If this section contains “System.Web.WebPages”,  update those elements from  version “2.0.0.0” to  version“3.0.0.0”

   <configuration>   <configSections>     <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">       <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />       <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />     </sectionGroup>   </configSections>

3. If you removed the Microsoft-Web-Helpers NuGet package in a  previous step, install Microsoft.AspNet.WebHelpers  with  the following command in the PMC:
   Install-Package -Id  Microsoft.AspNet.WebHelpers
4. If your app uses the  User.IsInRole() method, add the following to the Web.config file.

   <system.webServer>
       <modules>
         <remove name="RoleManager" />
       </modules>
     </system.webServer>

Final Steps

Build and test the application.

Remove the MVC 4 project type GUID from the project files.

1. In Solution Explorer, right-click the project name and then select Unload Project.
2. Right-click the project  and select Edit ProjectName.csproj.
3. Locate the ProjectTypeGuids element and then remove  the MVC 4 project GUID, {E3E379DF-F4C6-4180-9B81-6769533ABE47}.
4. Save and close the open project file.
5. Right-click the project and select Reload Project.