File encrypt and decrypt error - Test my code please to see if error can be found

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C#

I want to test the File.Encrypt and File.Decrypt methods but I am getting errors. Had a look at the MSDN site but no solution to my problem have I found. Am I missing something?

private void button2_Click(object sender, EventArgs e)
{
    File.Decrypt("Text.pvf");
    string[] DataFile = File.ReadAllLines("Text.pvf");
    if (DataFile[5] == "6")
        MessageBox.Show("Encrypt/Decrypt successful");
}

private void button1_Click(object sender, EventArgs e)
{
    string[] DataFile = new string[6];
    DataFile[0] = "1";
    DataFile[1] = "2";
    DataFile[2] = "3";
    DataFile[3] = "4";
    DataFile[4] = "5";
    DataFile[5] = "6";
    File.WriteAllLines("Text.pvf", DataFile);
    File.Encrypt("Text.pvf");
}

I am getting an error message when button1 is clicked, "File.Encrypt("Text.pvf");" returns an error exception, "The request is not supported."

Maybe copy my code to test it. Maybe that will help in determining the error.
Please help with this as I don't what the cause is