vb.net authorization error with AD and LDAP

We are upgrading our servers and .net application from windows 2000 to the newly-purchased windows 2012R2 servers. There is one function which works in windows 2000 but doesn’t work in windows 2012R2.

We are running an .net 2.0 internal application in windows 2000 and IIS 5.0 using Visual Studio professional 2015. There is one function in this application which will make a function call to an AD server using LDAP to check the login id and password in Active Directory. It is running perfectly fine before. However, once I upgrade to this new window2012R2 server running .net 2.0, it doesn’t work. The function in the application is not able to get authorization in the Active Directory. The function as below:

Private Function IsAuthenticatedByAD(ByVal sUid As String, ByVal sPwd As String) As Boolean

  Dim direntRoot As DirectoryEntry, direntUsr As DirectoryEntry
  Dim sDomain As String, sDomainAndUid As String
  Dim dirsrchUsr As DirectorySearcher, oNative As Object

  direntRoot = New DirectoryEntry("LDAP://rootDSE")
  sDomain = direntRoot.Properties("DefaultNamingContext")(0)

  sDomainAndUid = String.Format("{0}\{1}", sDomain, sUid)
  direntUsr = New DirectoryEntry(direntRoot.Path, sDomainAndUid, sPwd)

  Try
      oNative = direntUsr.NativeObject
  Catch ex As Exception
      Return False
  End Try

  Return True

End Function

I received error message in the "Try" section when run oNative = .... The error message as below:

"System.DirectoryServices.DirectoryServicesCOMException (0x8007052E): The user name or password is incorrect." & vbCrLf & vbCrLf & " at System.DirectoryServices.DirectoryEntry.Bind(Boolean throwIfFail)" & vbCrLf & " at System.DirectoryServices.DirectoryEntry.Bind()" & vbCrLf & " at System.DirectoryServices.DirectoryEntry.get_NativeObject()" & vbCrLf & " at ums.business.UsrMgmtBus.IsAuthenticatedByAD(String sUid, String sPwd) in C:\inetpub\wwwroot\ums\business\UsrMgmtBus.vb:line 127"

Please help. Thanks a lot.