title: Class library can't find MembershipUser
body: <p>I've added a class library project to my application.</p>
  
  <p>In one of my classes, I need to use the MembershipUser class, but the project can't find it. I've added references to System.Web, System.Web.Security, and System.Security.Principal.</p>
  
  <p>I'm not sure what the problem is. Has anyone run into this?</p>