How can we check disabled user in active directory?

i am working asp.net 2003. i use the following code. when the execution reaches to Dim obj As Object = entry.NativeObject then it will show the logon failure for the user. if it is disabled user. but if it is enabled user it will work fine.i want to check the idsabled user code. plese help me
Dim domainAndUsername As String = domain + "\" + username
  Dim entry As New DirectoryEntry(_path, domainAndUsername, pwd)
  Dim obj As Object = entry.NativeObject
  Dim search = New DirectorySearcher(entry)


  search.Filter = "(SAMAccountName=" + username + ")"
  search.PropertiesToLoad.Add("cn")
  search.PropertiesToLoad.Add("userAccountControl")
  Dim result As SearchResult = search.FindOne()
  If (result Is Nothing) Then Return False

  ' Update the new path to the user in the directory
  _path = result.Path
  _filterAttribute = result.Properties("cn")(0)

  If Not _filterAttribute Is Nothing Then
  Dim accountControl As Integer
  accountControl = Convert.ToInt32(result.Properties("userAccountControl")(0))
  Dim accountDisabled As Integer = Convert.ToInt32(UF_ACCOUNTDISABLE)
  Dim flagExists As Integer = accountControl And accountDisabled
  If flagExists > 0 Then
  Throw New Exception("User Account Is Disabled")
  Return False

  Else
  Return True
  End If

  End If