Eu tentaria algo assim:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
namespace ConsoleApplication5
{
class Program
{
static void Main(string[] args)
{
Delete(@"C:/" + caminho + "/tele_05-21-50", ".au");
}
private static void Delete(string folder, string extension)
{
string[] files = Directory.GetFiles(folder, "*" + extension, SearchOption.AllDirectories);
foreach (var file in files)
{
try
{
File.Delete(file);
}
catch (Exception ex)
{
Console.WriteLine("An exception to archive " + file + ". Exception " + ex.Message);
}
}
}
}
}