No puedo descargar archivos externos que sean demasiado grandes.asp.net

Tengo una WEB en la que ofrezco descargar videos personales

Al descargar imagenes y archivos relativamente pequenos no hay problema.
Pero si son muy grandes como 700 mb incluso menos, me da error.

esta es mi funcion:

Código:

  Dim reqFTP As FtpWebRequest
        Dim fileName As String = System.IO.Path.GetFileName(Me.UrlString)
        Dim descFilePath As String = System.IO.Path.Combine(Me.DestDir, fileName)

        Try
            reqFTP = DirectCast(FtpWebRequest.Create(Me.UrlString), FtpWebRequest)
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile
            reqFTP.UseBinary = True

            Using outputStream As New FileStream(descFilePath, FileMode.OpenOrCreate)
                Using response As FtpWebResponse = DirectCast(reqFTP.GetResponse(), FtpWebResponse)
                    Using ftpStream As Stream = response.GetResponseStream()
                        Dim bufferSize As Integer = 2048
                        Dim readCount As Integer
                        Dim buffer As Byte() = New Byte(bufferSize - 1) {}
                        readCount = ftpStream.Read(buffer, 0, bufferSize)
                        While readCount > 0
                            outputStream.Write(buffer, 0, readCount)
                            readCount = ftpStream.Read(buffer, 0, bufferSize)
                        End While
                    End Using

                End Using
            End Using
            Return True

        Catch ex As Exception
            Throw New Exception("Failed to download", ex.InnerException)
        End Try
    End Function

Alguien tiene idea de algun metodo de como descargar un archivo externo de 4gb via asp.net al PC del cliente.
Se agradecera alguna ayuda.

No me vale response.redirect(Tengo mis motivos)
Saludos.

Public Overrides Function DownloadFile() As Boolean
Dim fileName As String = System.IO.Path.GetFileName(Me.UrlString)
Dim descFilePath As String = System.IO.Path.Combine(Me.DestDir, fileName)
Try
Dim myre As WebRequest = WebRequest.Create(Me.UrlString)
Catch ex As Exception
Throw New Exception("File doesn't exist on server", ex.InnerException)
End Try
Try
Dim fileData As Byte()
Using client As New WebClient()
fileData = client.DownloadData(Me.UrlString)
End Using
Using fs As New FileStream(descFilePath, FileMode.OpenOrCreate)
fs.Write(fileData, 0, fileData.Length)
End Using
Return True
Catch ex As Exception
Throw New Exception("Failed to download", ex.InnerException)
End Try
End Function