Поток не поддерживает запись

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Извините, у меня есть программа, и я получил какую-то ошибку. есть ошибка в "

cs.Write(bytBuffer, 0, intBytesInCurrentBlock)

"Поток не поддерживает запись. Пожалуйста, помогите мне в учебе. спасибо, извините за мой плохой английский.

Что я уже пробовал:

Private Sub enkripataudekrip(ByVal inputfile As String, ByVal outputfile As String, ByVal secret As String, ByVal direction As aksikripto)

        Dim fsinput As New FileStream(inputfile, FileMode.Open, FileAccess.Read)
        Dim fsoutput As New FileStream(outputfile, FileMode.OpenOrCreate, FileAccess.Write)
        fsoutput.SetLength(0)
        Dim skey As String = "aaaaaaaa"
        Dim bytBuffer(4096) As Byte 'holds a block of bytes for processing
        Dim lngBytesProcessed As Long = 0 'running count of bytes processed
        Dim lngFileLength As Long = fsinput.Length 'the input file's length
        Dim intBytesInCurrentBlock As Integer 'current bytes being processed
        Dim cs As CryptoStream
        Dim des As New DESCryptoServiceProvider
        des.Key = ASCIIEncoding.ASCII.GetBytes(skey)
        des.IV = ASCIIEncoding.ASCII.GetBytes(skey)
        Select Case direction
            Case aksikripto.enkrip
                

                cs = New CryptoStream(fsoutput, des.CreateEncryptor, CryptoStreamMode.Write)
                'Dim bytearrayinput(fsinput.Length - 1) As Byte
                'fsinput.Read(bytearrayinput, 0, bytearrayinput.Length)
                'cs.Write(bytearrayinput, 0, bytearrayinput.Length)
                'cs.Close()

            Case aksikripto.dekrip
                'Dim des As New DESCryptoServiceProvider
                cs = New CryptoStream(fsinput, des.CreateDecryptor, CryptoStreamMode.Read)

                'Dim fsdekrip As New StreamWriter(outputfile)
                'fsdekrip.Write(New StreamReader(csdec).ReadToEnd)
                'fsdekrip.Flush()
                'fsdekrip.Close()
        End Select

        While lngBytesProcessed < lngFileLength
            intBytesInCurrentBlock = fsinput.Read(bytBuffer, 0, 4096)
            cs.Write(bytBuffer, 0, intBytesInCurrentBlock) 'Stream does not support writing

        End While

        cs.Close()
        fsinput.Close()
        fsoutput.Close()

    End Sub

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