Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0

So simple. In Nuget Package Manager Console:

Update-Package Microsoft.AspNet.Mvc -Reinstall

This problem started when I did 'Remove Unused References'. The website still worked on my local machine, but did not worked on the server after publishing.

https://i.stack.imgur.com/SRpQM.png

I fixed this problem by doing the following,

Open 'Package Manager Console' in Visual Studio Uninstall-Package Microsoft.AspNet.Mvc Install-Package Microsoft.AspNet.Mvc

how do I find out what is referencing System.Web.WebPages.Razor v2.0.0.0?

Just read your exception stacktrace:

Calling assembly : Microsoft.Web.Helpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35

So it seems that you are using the Microsoft.Web.Helpers which in turn depends on System.Web.WebPages.Razor, Version=2.0.0.0.

After much pain, googling and hair pulling, I ended up uninstalling MVC 4 using nuget, deleting all references to MVC, razor and infrastructure from the web config, deleting the dlls from the bin folder - then using nuget to reinstall everything. It took less time then trying to figure out why the dlls did not match.

In ASP.NET MVC 4, the namespace is not System.Web.WebPages.Razor, but System.Web.Razor

That worked for me, change your web.config.

I uninstalled ASP.NET MVC 4 using the Windows Control Panel, then reinstalled it by running AspNetMVC4Setup.exe (which I got from https://www.microsoft.com/en-us/download/details.aspx?id=30683), and that fixed the issue for me.

In other words, I didn't need to use Nuget or Visual Studio.

I was getting the same error after adding an unnecessary reference to System.Web.Mvc. I removed all the references I could find, but nothing seemed to work. I finally deleted the project's bin folder and the error went away after a rebuild.

I was getting the same error when i upgrade MVC4 to MVC5 version, Firstly i Upgraded the calling assembly which was depends on

> System.Web.WebPages.Razor, Version=2.0.0.0

after that updated the web.config files under the Views folder, updated following packages from

<configSections>
    <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
      <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
      <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
    </sectionGroup>
</configSections>

to

<configSections>
    <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, 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>

and also updated

<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />

to

<host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=5.2.7.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />

these steps works for me

I also received this error and tried everything I could find online and it wouldn't go away. In the end, I just downgraded MVC from 5.2.3 to 4.0.40804. I don't like this solution because eventually I'll need to use MVC 5, but it works for now. Hope this helps others.

Short: In you have this problem with a pure Web API project (and thus don't need razor), try to add it anyway, rebuild, then remove it.

Long story: I had this problem with a brand-new pure Web API project, except that the stacktrace pointed "System.Web.Mvc" as Calling assembly (see Darin's answer). No reference to MVC, Razor or anything like that in my project though... I decided to add the MVC packages (AspNet.Mvc, AspNet.WebPages and AspNet.Razor) to check if there was any subsequent problem. The WebApi app then launched perfectly fine. Then I removed the exact same packages and everything was still OK. Hope it helps someone.

After my PC got completely reinstalled, I got the error described here. VS 2017 was reinstalled but "ASP.NET Web Pages 2" was not reinstalled. After reinstalling "ASP.NET Web Pages 2", the problem was solved.

See also: Could not load file or assembly System.Web.WebPages.Razor, , Version=3.0.0.0 or one of its dependencies

In some cases, just install web page 2 to resolve this (resolved with my case - deploy to local web page using web api )

https://www.microsoft.com/en-us/download/details.aspx?id=34600

If earlier working project crashing suddenly with mentioned error you can try following solution.

Delete the bin folder of respective web/service project.

Build

This worked for me.

For similar assembly binding errors , following steps may help:

Right click on your Solution and click Manage Nuget Packages for Solution ... go to Consolidate Tab (last tab) and check if any any differences between packages installed in different projects inside your solution. specially pay attention to your referenced projects which may have lower versions because they usually are less noticed) consolidate specially packages related to your assembly error and note that many packages are dependent on some other packages like *.code & *.api & ... after resolving all suspected consolidations , rebuild and rerun the app and see if the assembly bindings are resolved.

I first tried Mohammed Emad's answer - no joy. Then I tried

git clean -x -d -f

which brought me to a new "Roslyn" error which I was able to fix by manually editing my .csproj.

Interestingly, after I'd read down a bit further down the page on the Roslyn question, I found another suggestion with even more votes (Update-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform -r). Thinking I'd rather implement that than manually edit .csproj, I backed out my .csproj changes, only to find my solution was still working.

So after all that, I'm wondering if Mohammed's answer (on this page) would have done the trick, had I simply done the git clean first.

by installing AspNetMVC4Setup.exe ( Here is the link :https://www.microsoft.com/en-us/download/details.aspx?id=30683) solves the issue.

by restart/reinstalling Microsoft.AspNet.Mvc Package doesn't help me.

I downgraded via NuGet to MVC 4 and then upgraded again to 5.2.7 and it fixed this issue

Fix Your Problem

Remove WebMatrix.Data and WebMatrix.WebData in the References of your Project