title: What is a "could not find type System.Collections.Generic.List" in the .NET Designer?
body: <p>I've got a WinForms project that I've had for quite some time, and now suddenly, I can't open the designer anymore and when I try to open the designer I get an error that says</p>
  
  <p>could not find type 'System.Collections.Generic.List'</p>
  
  <p>All of the code builds just fine, but I can't use the designer anymore, and I don't know what happened, nor do I have any idea where to look to solve the problem. Has anyone ever run into this or have any insight?</p>