“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

For me, the problem occure when I add asynchronous method with async Task await in my .net4.0 project !

With previous versions of the .NET-Framework 4.5, you must install this package:

Install-package Microsoft.Bcl.Async –pre

or

Install-Package Microsoft.CompilerServices.AsyncTargetingPack

more info on Nuget or Nuget