VB.Net: Returning AD UserName from Multi-Domain Forrest

Growth sometimes brings out the unexpected flaws in designs. What seems like a quick solution, may intern lead to what I have affectionately call 'Learning Opportunities'.After a recent expansion from a single domain environment to a multi-domain forest, the following VB.Net function ceased functioning for retrieving the user's full name.

Public Shared Function GetADUserName() As String
    Dim returnString As String = String.Empty     
        If HttpContext.Current.User.Identity.IsAuthenticated Then     
            Try
               Dim DomainUser As String = WindowsIdentity.GetCurrent.Name.Replace("\", "/")
               Dim ADEntry As New DirectoryEntry("WinNT://" & DomainUser)
               Dim FullName As String = ADEntry.Properties("FullName").Value

               returnString = FullName.Substring(FullName.LastIndexOf(",") + 1)
               returnString &= " " & FullName.Substring(0, FullName.LastIndexOf(","))
            Catch ex As Exception

            Finally

            End Try
      End If
      Return returnString
End Function

Doing some research resulted in the realization that the WinNT provider would only work correctly in a 'flat domain'. Some modifications to an existing application allowed for the following replacement utilizing the LDAP provider in the DirectoryServices library. The key is to enable Referral Chasing.

Public Shared Function GetADUserName() As String
   Dim returnString As String = String.Empty       
      If HttpContext.Current.User.Identity.IsAuthenticated Then           
         Try                
             ' Set the root search path
             Dim ldapPath As String = "LDAP://DC=MyDomain,DC=COM"    
             Dim entry As New DirectoryEntry(ldapPath)
            ' AppSettings holds username and password
            ' This allows the query to run outside the context of the impersonated user
            ' This user currently is delegated rights in AD               
            entry.Username = ConfigurationManager.AppSettings("AdUser").ToString
            entry.Password = ConfigurationManager.AppSettings("ADPassword").ToString
            entry.AuthenticationType = AuthenticationTypes.Secure
           
            ' Retrieve the current user's ntid               
            Dim DomainUser As String = WindowsIdentity.GetCurrent.Name.Substring
                         (WindowsIdentity.GetCurrent.Name.LastIndexOf("\"))

            ' Set your filter
            Dim filter As String = 
                   String.Format("(&(objectClass=user)(sAMAccountName={0}))", DomainUser)
            Dim searcher As New DirectorySearcher(entry, filter, New String() {"displayName"})

           ' Allow searches to span multiple domain referrals
           searcher.ReferralChasing = ReferralChasingOption.All
           Dim result As SearchResult = searcher.FindOne()

          If Not IsNothing(result) Then
             'Verify the property was returned
             If (result.Properties.Contains("displayName")) Then
                returnString = result.Properties("displayName")(0)
             End If
          End If
       Catch ex As Exception
           'Some error handling here
       Finally
  
       End Try
   End If
   
   Return returnString
End Function