Well I tried with this options and it shows the same error.

string script = File.ReadAllText(sqlCommandFilePath, System.Text.Encoding.ASCII);

string script = File.ReadAllText(sqlCommandFilePath, System.Text.Encoding.Unicode);

string script = File.ReadAllText(sqlCommandFilePath, System.Text.Encoding.UTF32);

string script = File.ReadAllText(sqlCommandFilePath, System.Text.Encoding.UTF7);

string script = File.ReadAllText(sqlCommandFilePath, System.Text.Encoding.UTF8);

But System.Text.Encoding doesn't show ANSI to choose from the list.