System.DirectoryServices.AccountManagement.UserPrincipal - localhost but not iis

Question

Why does the code below work fine when I run my web application localhost but not when I install it to an IIS server?

using (HostingEnvironment.Impersonate())
{
    UserPrincipal activeUser = UserPrincipal.Current;
    String activeUserSid = activeUser.Sid.ToString();
    String activeUserUPN = activeUser.UserPrincipalName;
}

Please don't suggest I stick with HttpContext.Current.User as it doesn't provide access to SID or UPN without additional calls to Active Directory.

The web application will be used by Windows authenticated users from three separate domains, the web server is hosted in a fourth domain. The Application Pool is configured to run under the NetworkService identity and the web app configuration has identity impersonation set to true.

The error message when it runs on IIS is:

Error in Page_Load(): UserPrincipal.Current.
System.InvalidCastException: Unable to cast object of type 'System.DirectoryServices.AccountManagement.GroupPrincipal' to type 'System.DirectoryServices.AccountManagement.UserPrincipal'.
at System.DirectoryServices.AccountManagement.UserPrincipal.FindByIdentity(PrincipalContext context, IdentityType identityType, String identityValue)
at System.DirectoryServices.AccountManagement.UserPrincipal.get_Current()
at webapp.Details.Default.Page_Load(Object sender, EventArgs e)

EDIT: Tried both the following and unfortunately get the same error.

UserPrincipal userPrincipal = UserPrincipal.Current;
Response.Write(userPrincipal.Name);

Principal userOrGroup = UserPrincipal.Current;
Response.Write(userOrGroup.Name);

Answer 1

I had a lot of issues deploying UserPrincipal.Current and still don't fully understand why.

I finally ended up using PrincipalSearcher, and created the following function to do what I thought UserPrincipal.Current was doing.

private UserPrincipal GetActiveDirectoryUser(string userName)
{
    using(var ctx = new PrincipalContext(ContextType.Domain))
    using(var user = new UserPrincipal(ctx) { SamAccountName = userName})
    using(var searcher = new PrincipalSearcher(user))
    {
        return searcher.FindOne() as UserPrincipal;
    }
}

And I passed System.Web.HttpContext.Current.User.Identity.Name into that method as the userName.