# asp.net – Could not load file or assembly System.Web.Http.WebHost after published to Azure web site

## The Question :

144 people think this question is useful

I created a web project and it runs well in Visual studio. However, I got the following error after published it to azurewebsites. What can cause the issue?

Could not load file or assembly ‘System.Web.Http.WebHost, Version=5.0.0.0, 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.Http.WebHost, Version=5.0.0.0, 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.

WRN: Assembly binding logging is turned OFF. To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1. Note: There is some performance penalty associated with assembly bind failure logging. To turn this feature off, remove the registry value [HKLM\Software\Microsoft\Fusion!EnableLog].

The following is part of web.config file.

  <system.web>
<customErrors mode="Off"/>
<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" />
<authentication mode="Forms">
</authentication>
<pages>
<namespaces>
</namespaces>
</pages>
</system.web>
<system.webServer>
<validation validateIntegratedModeConfiguration="false" />
<handlers>
<remove name="ExtensionlessUrlHandler-ISAPI-4.0_32bit" />
<remove name="ExtensionlessUrlHandler-ISAPI-4.0_64bit" />
<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
</handlers></system.webServer>
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="DotNetOpenAuth.Core" publicKeyToken="2780ccd10d57b246" />
<bindingRedirect oldVersion="1.0.0.0-4.0.0.0" newVersion="4.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="DotNetOpenAuth.AspNet" publicKeyToken="2780ccd10d57b246" />
<bindingRedirect oldVersion="1.0.0.0-4.0.0.0" newVersion="4.1.0.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="2.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="1.0.0.0-4.0.0.0" newVersion="4.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="2.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-1.5.2.14234" newVersion="1.5.2.14234" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="EntityFramework" publicKeyToken="b77a5c561934e089" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.0.0.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>



131 people think this answer is useful

The dll is missing in the published (deployed environment). That is the reason why it is working in the local i.e. Visual Studio but not in the Azure Website Environment.

Just do Copy Local = true in the properties for the assembly(System.Web.Http.WebHost) and then do a redeploy, it should work fine.

If you get the similar error i.e. some other assembly missing, then make that assembly to copylocal=true and redeploy, repeat this iteratively – if you are unsure of its dependencies.

91 people think this answer is useful

If you are still looking for an answer, try checking this question thread. It helped me resolve a similar problem.

edit: The solution that helped me was to run Update-Package Microsoft.AspNet.WebApi -reinstall from the NugGet package manager, as suggested by Pathoschild. I then had to delete my .suo file and restart VS, as suggested by Sergey Osypchuk in this thread.

55 people think this answer is useful

I met the same problem and I resolved it by setting CopyLocal to true for the following libs:

System.Web.Http.dll
System.Web.Http.WebHost.dll
System.Net.Http.Formatting.dll



I must add that I use MVC4 and NET 4

34 people think this answer is useful

For me worked adding the following section to web.config file:

<configuration>
...
<runtime>
...
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-5.1.0.0" newVersion="5.1.0.0" />
</dependentAssembly>
...
</runtime>
...
</configuration>



This example stands for MVC 5.1. Hope it will help someone to resolve such issue.

16 people think this answer is useful

For me it started working after selecting “Remove additional files at destination” in File publish options under settings on the publish dialog.

10 people think this answer is useful

The dll is missing in the published (deployed environment). That is the reason why it is working in the local i.e. Visual Studio but not in the Azure Website Environment.

Just do Copy Local = true in the properties for the assembly(System.Web.Http.WebHost) and then do a redeploy, it should work fine.

6 people think this answer is useful

I’m using vs2012 and i think the update KB2781514 changed some setting. All my System.Web.Http in my MVC4 project changed to false and i keeping received this message. I had changed the All file in this project in publish property but its not working. Finally I have to change Copy Local = true one by one and solved this problem.

2 people think this answer is useful

I got the same error and I changed my version from 4 to 3 and it is solved:

<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<!-- Ensure correct version of MVC -->
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0"/>
</dependentAssembly>
</assemblyBinding>



2 people think this answer is useful

I had the same problem in my Application.

System.web.http.webhost not found.



You just need to copy the system.web.http.webhost file from your main project which you run in Visual Studio and paste it into your published project bin directory.

After this it may show the same error but the directory name is changed it may be system.web.http. Follow same procedure as above. It will work after all the files are uploaded. This due to the nuget package in Visual Studio they download from the internet but on server it not able to download it.

You can find this file in your project bin directory.

1 people think this answer is useful

This happened to me on VS2013(Update 5)/ASP.NET 4.5, under project type “Web Application” that includes MVC and Web API 2. Error happened right after creating the project and before adding any code. Adding the following configuration fix it for me. After resolving “System.Web.Helpers” issue two more similar errors surfaced for “System.Web.Mvc” and “System.Web.WebPages”.

<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-2.0.0.0" newVersion="2.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.2.3.0" />
</dependentAssembly>
<dependentAssembly>
<bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>



0 people think this answer is useful

I was missing several DLLs. Even if I manually copied them to the directory the next time I published they would disappear. Each one was already set to Copy Locally in VS. The fix for me was to set each one to Copy Locally false, save, build then set each one to copy locally true. This time when I published all of the DLLs published correctly. Strange

0 people think this answer is useful

If you have multiple projects in your solution and one of your projects fails to build because of this error then ensure you have installed the WebApi Core nuget package in that project. Simply adding a reference to the System.Web.Http does not help, you need to install the correct nuget package into that project.

I had multiple projects in my solution and WebApi Core was already installed in another project. I referenced the System.Web.Http assembly by right-clicking and ticking the assembly from the list and it did not work on Azure, though locally it would build okay. I had to remove the manual reference and add the WebApi Core nuget package to each project that needed the assembly reference.

0 people think this answer is useful

In the case if “Copy Local” is already True, I find it sometimes to work if you remove the files where it has been published to and publish again.

For example if you’re using IIS, remove the websites and the contents of the directory to which they are published to, and publish again.

There might be older versions of files at the destination, so to ensure you aren’t using older versions, delete everything before publishing again.

0 people think this answer is useful

I removed the following entry from web.config and it worked for me.

<dependentAssembly>

Make sure the package version is equal across the solution. I just downgraded & upgraded Microsoft.AspNet.Mvc package across the solution and the problem solved.