Could not load file or assembly 'System.Web.We

Question

I just upgraded packages in an MVC 3 project (ASP.net 4), and now I am getting the following error message when accessing a page in that project:

Server Error in '/MyApplication' Application.

Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040) 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.IO.FileLoadException: Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Assembly Load Trace: The following information can be helpful to determine why the assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' could not be loaded.

=== Pre-bind state information === LOG: User = IIS APPPOOL\ASP.NET v4.0 LOG: DisplayName = System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 (Fully-specified) LOG: Appbase = file:///C:/.../ LOG: Initial PrivatePath = C:...\bin Calling assembly : Microsoft.Web.Helpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35. === LOG: This bind starts in default load context. LOG: Using application configuration file: C:...\web.config LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet.config LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\v4.0.30319\config\machine.config. LOG: Post-policy reference: System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/.../cb62a7b2/327a0353/System.Web.WebPages.Razor.DLL. LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/.../cb62a7b2/327a0353/System.Web.WebPages.Razor/System.Web.WebPages.Razor.DLL. LOG: Attempting download of new URL file:///C:/LeGroupeHtmSVN/.../UpDir.Web/bin/System.Web.WebPages.Razor.DLL. WRN: Comparing the assembly name resulted in the mismatch: Major Version ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.

Stack Trace:

[FileLoadException: Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
Microsoft.Web.Helpers.PreApplicationStartCode.Start() +0

[InvalidOperationException: The pre-application start initialization method Start on type Microsoft.Web.Helpers.PreApplicationStartCode threw an exception with the following error message: Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040).]
System.Web.Compilation.BuildManager.InvokePreStartInitMethods(ICollection`1 methods) [phone]
System.Web.Compilation.BuildManager.CallPreStartInitMethods() +465
System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +1167

[HttpException (0x80004005): The pre-application start initialization method Start on type Microsoft.Web.Helpers.PreApplicationStartCode threw an exception with the following error message: Could not load file or assembly 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040).]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) [phone] System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +141 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4869125

-------------------------------------------------------------------------------- Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.272

In my web.config file, and in my application, I am referencing System.Web.WebPages.Razor v1.0.0.0:

  <dependentAssembly>
    <assemblyIdentity name="System.Web.WebPages.Razor" publicKeyToken="31bf3856ad364e35" culture="neutral" />
    <bindingRedirect oldVersion="0.0.0.0-1.0.0.0" newVersion="1.0.0.0" />
  </dependentAssembly>

I don't even know whether I could be using System.Web.WebPages.Razor v2.0.0.0 with .Net 4.

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

Answer 1

So simple. In Nuget Package Manager Console:

Update-Package Microsoft.AspNet.Mvc -Reinstall

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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.