Modifica la creaFile cosi'

codice:
public void creaFile() 
{ 
	try 
	{ 
		string file = System.Text.Encoding.ASCII.GetString(ar);
		StreamWriter crea = new StreamWriter  ("C:/destinazione.txt"); 
		crea.Write(file); 
		crea.Close();
	} 
	catch (Exception ex) 
	{ 
		MessageBox.Show(ex.Message + ex.StackTrace); 
	} 
}