Could not load file or assembly Microsoft.CodeAnalysis.CSharp, Version= when deploying only


I have a Visual Studio solution with an web application project and a class library project alongside it.

The applications runs fine when I debug it in Visual Studio, however when I deploy it using WebDeploy, I get the following exception when loading the page:

Could not load file or assembly 'Microsoft.CodeAnalysis.CSharp, Version=, 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)

This also happens when deploying to a Folder.

My web project references Microsoft.CodeAnalysis.CSharp version 3.0.0, installed via Nuget and I can see it in the packages folder. Web.config contains this:

  <assemblyIdentity name="Microsoft.CodeAnalysis.CSharp" publicKeyToken="31bf3856ad364e35" culture="neutral" />
  <bindingRedirect oldVersion="" newVersion="" />

Super confused- I don't see any references anywhere and I don't know how I'm supposed to resolve this. I even tried manually installing version of Microsoft.CodeAnalysis.CSharp alongside the current version and nothing changes.


Okay so this appears to be resolved by turning the "Precompile during publish" option off when deploying. Hesitant to answer my own post with this because I suspect this is not a real solution.

asked on Stack Overflow Apr 30, 2019 by Mik • edited May 1, 2019 by Mik

2 Answers


In case you are using an older version of Microsoft.CodeDom.Providers.DotNetCompilerPlatform nuget, you can update that and try deploying again.

Microsoft.CodeDom.Providers.DotNetCompilerPlatform also references Microsoft.CodeAnalysis.CSharp

answered on Stack Overflow Apr 30, 2019 by akg179

There are a few different causes that have this sort out output, one of the main ones is when the main project, in your case the web application, does not have a specific reference to the dlls in question, and you are assuming that the build and deployment pipeline will correctly pickup all the dlls from the output of any dependant projects directly into the deployment package.

When nuget references are used in the satellite assemblies they are not automatically copied across. The main project needs specific pointers in the deployment scripts to know where to source the correct dlls from.

You may experience this issue on some dev boxes and not others for the same solution, or when you compare the dll outputs from both the satellite project and the web project that you are deploying you see that the web project has different versions of the dependant dlls

  1. Make sure that you install ALL nuget packages that are installed in your satellite projects into the main web project.

    • This helps the nuget package manager to detect clashes between dependencies and to automatically manage the binding redirect statements that may be required.
  2. Make sure that the same versions of packages in the satellite projects are installed in the main project.

    • Once the packages are installed you can use the Consolidate interface to detect and resolve version mismatches.
      • A version mismatch is ultimately what we are trying to avoid here.

If all of the above is correct, then you should look at the binding redirects in the web.config. This can be involved, instead start first with reinstalling all the nuget packages.

This can work because the installation scripts for nuget packages will automatically set binding redirects that may be necessary for your combination of dependancies

  1. Remove the assemblyBinding node from web.config if it is already there. Start fresh.

  2. npm: (where MyProject is the name of your web project)

    update-Package -ProjectName MyProject -reinstall 

That should do the trick!

ASP.NET web projects and other projects that have in-built deployment pipelines exhibit these issues more than other project types. Only the compiled dlls from the dependant projects are copied directly into the output of the deployment project, any nuget references for additional dependencies are expected to be resolved in the deployment project, otherwise if there are similar named assemblies in the GAC they will be used instead.

Using Strongly Named references can assist in avoiding these issues but that is usually a lot harder solution to implement if you use a lot of 3rd party assemblies that are not strongly named.

This was an ironic experience for me as the cause and solution are similar to my very first post on SO: Azure package not including linked project DLL even with copy local set its a slightly different flavour but I should have known better by now!

answered on Stack Overflow Jul 13, 2020 by Chris Schaller • edited Jul 13, 2020 by Chris Schaller

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