verdiğiniz kod için denemedim ama olması lazım
<%
' Functions for encoding string to Base64
Function Base64Encode(sText)
  Dim oXML, oNode
  Set oXML = CreateObject("Msxml2.DOMDocument.3.0")
  Set oNode = oXML.CreateElement("base64")
  oNode.dataType = "bin.base64"
  oNode.nodeTypedValue = Stream_StringToBinary(sText)
  Base64Encode = oNode.text
  Set oNode = Nothing
  Set oXML = Nothing
End Function

Function Base64Decode(ByVal vCode)
  Dim oXML, oNode
  Set oXML = CreateObject("Msxml2.DOMDocument.3.0")
  Set oNode = oXML.CreateElement("base64")
  oNode.dataType = "bin.base64"
  oNode.text = vCode
  Base64Decode = Stream_BinaryToString(oNode.nodeTypedValue)
  Set oNode = Nothing
  Set oXML = Nothing
End Function

Private Function Stream_StringToBinary(Text)
  Const adTypeText = 2
  Const adTypeBinary = 1
  Dim BinaryStream 'As New Stream
  Set BinaryStream = CreateObject("ADODB.Stream")
  BinaryStream.Type = adTypeText
  BinaryStream.CharSet = "us-ascii"
  BinaryStream.Open
  BinaryStream.WriteText Text
  BinaryStream.Position = 0
  BinaryStream.Type = adTypeBinary
  BinaryStream.Position = 0
  Stream_StringToBinary = BinaryStream.Read
  Set BinaryStream = Nothing
End Function

Private Function Stream_BinaryToString(Binary)
  Const adTypeText = 2
  Const adTypeBinary = 1
  Dim BinaryStream 'As New Stream
  Set BinaryStream = CreateObject("ADODB.Stream")
  BinaryStream.Type = adTypeBinary
  BinaryStream.Open
  BinaryStream.Write Binary
  BinaryStream.Position = 0
  BinaryStream.Type = adTypeText
  BinaryStream.CharSet = "us-ascii"
  Stream_BinaryToString = BinaryStream.ReadText
  Set BinaryStream = Nothing
End Function    


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