'Could not load file or assembly 'netstandard, Version=2.0.0.0, ...'. Reference assemblies should not be loaded for execution

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Goal: From a .NET 4.7 console app, using reflection with Assembly.GetType(), I am trying extract the Type of a netstandard 2.0 class from Assembly X. Then I want to create an instance of this Type with Activator.CreateInstance().

What I am trying to do: However, this assembly X has a dependency to netstandard 2.0. To be able to get the Type, netstandard dependency has to be loaded into the AppDomain. That's why when the AppDomain is requesting the netstandard assembly through the AssemblyResolve event, I simply load the dll like this :

var netStandardDllPath = @"C:\Users\xxx\.nuget\packages\NETStandard.Library.2.0.0-preview1-25301-01\build\netstandard2.0\ref\netstandard.dll";

return Assembly.LoadFrom(netStandardDllPath);

Which throws:

System.BadImageFormatException: 'Could not load file or assembly 'file:///C:\Users\vincent.lerouvillois.nuget\packages\NETStandard.Library.2.0.0-preview1-25301-01\build\netstandard2.0\ref\netstandard.dll' or one of its dependencies. Reference assemblies should not be loaded for execution. They can only be loaded in the Reflection-only loader context. (Exception from HRESULT: 0x80131058)'

Inner Exception: BadImageFormatException: Cannot load a reference assembly for execution.

What I know: I know that they want us to load the DLL with Assembly.ReflectionOnlyLoadFrom. But doing that will prevent me from instanciate the type with Activator.CreateInstance(). See Microsoft official post

Also, I tried referencing the Nuget packages NETStandard.Library 2.0.0-preview1-25301-01 and NETStandard.Library.NETFramework 2.0.0-preview1-25305-02 in my console app so it would have the netstandard 2.0 libraries referenced, but it didn't change anything.

Question: Does anyone would know if there is a proper way to load that dll without error, or maybe if this is a bug, or else? Or why this kind of dll is not able to load for execution?

.net-standard .net-assembly dll .net c#
9 Answers

Wow. I just spent several hours tracking the cause of this "could not load ... netstandard" error down.

For me, the problem was that my .NET Framework project (which references both .NET Framework and .NET Standard libraries) was built with .NET Framework 4.7.2 and the system where I was deploying and running it did not have 4.7.2 installed.

Deploying a very small Console project with the same basic structure and references and executing that in a Command window finally revealed the correct error, in a pop-up, that .NET Framework 4.7.2 was missing.

If you're struggling with this particular error, make sure you have the necessary .NET Framework installed.

user_52484000

Set Copy Local to true in netstandard.dll properties.

  1. Open Solution Explorer and right click on netstandard.dll.
  2. Set Copy Local to true.

enter image description here

user_28754550

For me solved doing the following: 1 - Installed latest .Net Framework on server. 2 - Updated windows server and my local machine. 3 - Went to Manage Nuget Package and updated all references on the update tab.

Perhaps only doing step 3 can solve in your case

user_27123490

In case if IBM Message Queue references are used in the project solution, this exception indicates that the DLL used for refering MQ classes are incompatible with the host(server) .NET version installed.

In this scenario, either we need to update server with latest update and make sure .NET latest version is available or use lower version of IBM Message queue DLL as reference.

Old version DLL - amqmdnet.dll (no new features will be introduced by IBM as not in support)

Latest version DLL - amqmdnetstd.dll (to run IBM MQ classes for .NET Standard, you must install Microsoft .NET Core)

user_136975630

Install NetStandard.Library 2.0.0.0 from NuGet , It works for me. when I downgrade .net framework 4.6.1 to 4.6.0

user_107192470

If you are having this issue for a project that used to work, try deleting the bin and obj folders since caching can cause this, too.

user_46259460
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