title: "Missing compiler required member" error being thrown multiple times with almost no changes to code
body: <p>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:</p>
  
  <blockquote>
    <p>Missing compiler required member System.Runtime.CompilerServices.ExtensionAttribute..ctor</p>
  </blockquote>
  
  <p>The error is a bit vague (other than it's description, obviously) as it doesn't give me a file, line, or column to reference, only the project. Also, it throws the error a total of 20 times. I only made three changes to the code between the time I deployed (it was completely functional at that time) and now. I reverted my changes and it is still throwing the same error which makes no sense to me.</p>
  
  <p>I haven't found a lot of information on this error on SO or Google, other than <a href="http://blog.flexforcefive.com/?p=105" rel="noreferrer">this guys</a> solution and a couple references to some Mono project errors (I'm not using Mono). The solution the guy above gives requires adding a class definition that will allow the compiler to resolve the reference. I don't particularly want to do this because I haven't needed to do it up until this point and it will just muddy my code. </p>
  
  <p>Just curious if anyone has run across this before. Thanks in advance!</p>