VB.net Datei beim Download über Socket durch 5 wiederkehrende Zeichen beschädigt

        Sub Start()
            Dim IP As IPAddress
            Dim URL2 As String = RegularExpressions.Regex.Match(_URLStart, "(http|https)://(.*?)(:[0-9])?/").Groups(2).Value  
            Dim PORT As String = RegularExpressions.Regex.Match(_URLStart, "(http|https)://(.*?)(:[0-9])?/").Groups(3).Value  
            IP = IPAddress.Parse(URL2) : If PORT = "" Then PORT = 80  
            Dim IPEP As IPEndPoint = New IPEndPoint(IP, PORT)

            _Sock = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
            _Sock.Connect(IPEP) : Thread.Sleep(50) : If _Sock.Connected = False Then Exit Sub
            _Sock.ReceiveTimeout = 60000 : _Sock.SendTimeout = 1000

            Dim Header As New StringBuilder
            Header.AppendLine("GET " & Mid(_URLStart, InStr(_URLStart, IP.ToString) + IP.ToString.Length) & " HTTP/1.1")  
            Header.AppendLine("Host: " & IP.ToString)  
            Header.AppendLine("Connection: keep-alive")  
            Header.AppendLine() : _Sock.Send(Encoding.UTF8.GetBytes(Header.ToString))

            Do Until _Sock.Connected = False
                Dim B(_Sock.Available - 1) As Byte : _Sock.Receive(B)
                _MS.Write(B, 0, B.Length) : Thread.Sleep(50)
            Loop
        End Sub

HTTP/1.1 200 OK
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-type: application/octet-stream
Date: Thu, 03 May 2018 19:42:06 GMT
Keep-Alive: timeout=60, max=300
Content-Disposition: attachment; filename=export.ext