Visual Studio: Instance object was created as immutable error

I was working in adding a .dll in the Visual studio and got “Instance object was created as immutable” error message.

Just thought to add a short note to tell you how I fixed it, so in future if anyone gets an error knows how to fix it.

You need to add a reference to the NetStandard.Library NuGet Package, before you can add a .netstandard library.

Then add references to the DLL.

And that worked perfectly well… !!