Why am I getting a NullReferenceException from Membership.GetCurrentUserName ?

I've just switched to using msbuild to precompile my website and now I'm getting this strange error:

I have a call to Membership.GetUser() which throws:

[NullReferenceException: Object reference not set to an instance of an object.]
System.Web.Security.Membership.GetCurrentUserName() +36
System.Web.Security.Membership.GetUser() +7
...

From stackoverflow

• Reflector shows the implementation of Membership.GetCurrentUserName is:

  private static string GetCurrentUserName()
  {
      if (HostingEnvironment.IsHosted)
      {
          HttpContext current = HttpContext.Current;
          if (current != null)
          {
              return current.User.Identity.Name;
          }
      }
      IPrincipal currentPrincipal = Thread.CurrentPrincipal;
      if ((currentPrincipal != null) && (currentPrincipal.Identity != null))
      {
          return currentPrincipal.Identity.Name;
      }
      return string.Empty;
  }
  

  At first glance the most likely explanation is that:

  • HttpContext.Current is not null, and

  • HttpContext.Current.User is null or has a null Identity property.

  All other paths seem to have a test for null.

  So I suggest you trace the type and contents of HttpContext.User.

  HttpContext.Current.User is an IPrincipal, and most concrete implementations of IPrincipal that I know of don't allow a null identity, so I'd bet on HttpContext.User being null.