Could not load file or assembly… NuGet Assembly Redirects

When working in larger projects, you will sometimes encounter errors similar to this one: “Could not load file or assembly 'Newtonsoft.Json, Version=4.5.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies. The system cannot find the file specified.” Or how about this one? “System.IO.FileLoadException : Could not load file or assembly 'Moq, Version=3.1.416.3, Culture=neutral, PublicKeyToken=69f491c39445e920' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Search all you want, most things you find on the Internet are from the pre-NuGet era and don’t really help. What now? In this post, let’s go over why this error sometimes happens. And I’ll end with a beautiful little trick that fixes this issue when you encounter it. Let’s go!

Redirecting Assembly Versions

In 90% of the cases, the errors mentioned earlier are caused by faulty assembly redirects. What are those, you ask? A long answer is on MSDN, a short answer is that assembly redirects let us trick .NET into believing that assembly A is actually assembly B. Or in other words, we can tell .NET to work with Newtonsoft.Json 6.0.0.4 whenever any other reference requires an older version of Newtonsoft.Json.

Assembly redirects are often created by NuGet, to solve versioning issues. Here’s an example which I took from an application’s Web.config:

<?xml version="1.0" encoding="utf-8"?> <configuration> <!-- ... --> <runtime> <legacyHMACWarning enabled="0" /> <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> <dependentAssembly> <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" /> <bindingRedirect oldVersion="0.0.0.0-6.0.0.0" newVersion="6.0.0.0" /> </dependentAssembly> </assemblyBinding> </runtime> </configuration>

When running an application with this config file, it will trick any assembly that wants to use any version < 6.0.0.0 of Newtonsoft.Json into working with the latest 6.0.0.0 version. Neat, as it solves dependency hell where two assemblies require a different version of a common assembly dependency. But… does it solve that?

NuGet and Assembly Redirects

The cool thing about NuGet is that it auto-detects whenever assembly redirects are needed, and adds them to the Web.config or App.config file of your project. However, this not always works well. Sometimes, old binding redirects are not removed. Sometimes, none are added at all. Resulting in fine errors like the ones I opened this post with. At compile time. Or worse! When running the application.

One way of solving this is manually checking all binding redirects in all configuration files you have in your project, checking assembly versions and so on. But here comes the trick: we can let NuGet do this for us!

All we have to do is this:

  1. From any .config file, remove the <assemblyBinding> element and its child elements. In other words: strip your app from assembly binding redirects.
  2. Open the Package Manager Console in Visual Studio. This can be done from the View | Other Windows | Package Manager Console menu.
  3. Type this one, magical command that solves it all: Get-Project -All | Add-BindingRedirect. I repeat: Get-Project -All | Add-BindingRedirect

NuGet Add Binding Redirect

NuGet will get all projects and for every project, add the correct assembly binding redirects again. Compile, run, and continue your day without rage. Enjoy!

PS: For the other cases where this trick does not help, check Damir Dobric’s post on troubleshooting NuGet references.

This is an imported post. It was imported from my old blog using an automated tool and may contain formatting errors and/or broken images.

Leave a Comment

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7 responses

  1. Avatar for Special K
    Special K February 13th, 2015

    Well done... saved me some heartache. Thanks for the post.

  2. Avatar for Mac
    Mac April 13th, 2015

    This didn't work for me, unfortunately.

  3. Avatar for sagor
    sagor June 19th, 2016

    i like this post

  4. Avatar for Bas Haasnoot
    Bas Haasnoot February 22nd, 2018

    Very nice article, after reading only the first few paragraphs I understood what i had to do to fix my issue.
    Thanks for this!

  5. Avatar for Bogdan Stojanovic
    Bogdan Stojanovic October 3rd, 2018

    Thanks a lot Maarten. This saved my day!

  6. Avatar for Josh Mouch
    Josh Mouch October 23rd, 2018

    This doesn’t work for “PackageReference” format. It only works for “package.config” format.

  7. Avatar for Maarten Balliauw
    Maarten Balliauw October 24th, 2018

    True. This post predates ProjectReferences though (2014).