“Missing compiler required member” error being thrown multiple times with almost no changes to code

Question

Today after deploying some changes to a C# MVC site that I run, I went back to make some more modifications and came across this error:

Missing compil

Answer 1

In my case it was because the project was not referencing Microsoft.CSharp. Once I added a reference to that assembly, it compiled just fine.

Answer 2

Probably you use dynamic keyword In .NetStandard Class library project. If so, you need to add a reference to Microsoft.CSharp library in the project. Hope it will resolve your problem.

Answer 3

NLog.dll 2.0 referenced from a .NET 4.0 project can cause this too.

Answer 4

I hit the same set of exceptions after I added some async methods to a winforms project. I needed to bump my .NET version from 4 to 4.5

Answer 5

This error usually means either your project is compiling against .NET 2.0 or you aren't referencing the correct version of System.Core.dll

For a near duplicate question, see Error when using extension methods in C#

Answer 6

Got this error when trying to use async Tasks against .NET 4.0. Updating Target Framework to 4.5.2 fixed the problem.