C# zip 压缩及解压缩

我在WINFORM 窗体上加了2个按钮
     private void button4_Click(object sender, EventArgs e)
        {
             string []FileProperties=new string[2];
             FileProperties[0] =txtFilePath.Text;//待压缩文件目录 
               FileProperties[1]="D:\\a.zip";  //压缩后的目标文件 
              UnZipClass Zc=new  UnZipClass (); 
              Zc.ZipFileMain(FileProperties);         }
        private void button5_Click(object sender, EventArgs e)
        {
              string []FileProperties=new string[2]; 
             FileProperties[0]=txtzip.Text;//待解压的文件 
             FileProperties[1]="D:\\" ;//解压后放置的目标目录 
            UnZipClass UnZc=new UnZipClass();
            string path="D:\\";
            UnZc.UnZip(txtzip.Text,path); 
        }我的DLL 层
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Diagnostics;
using System.Runtime.Serialization.Formatters.Binary;
using System.Data;
using System.Collections;
using ICSharpCode.SharpZipLib.BZip2;
using ICSharpCode.SharpZipLib.Zip;
using ICSharpCode.SharpZipLib.Zip.Compression;
using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
using ICSharpCode.SharpZipLib.GZip;
using ICSharpCode.SharpZipLib.Checksums;
namespace DLL
{  
    public class UnZipClass
    {
        /// <summary> 
        /// 解压文件 
        /// </summary> 
        public void UnZip(string filename,string path)
        {
            ZipInputStream s = new ZipInputStream(File.OpenRead(filename));
            ZipEntry theEntry;
            while ((theEntry = s.GetNextEntry()) != null)
            {
                string directoryName = path;
                string fileName = Path.GetFileName(theEntry.Name);
                //生成解压目录 
                Directory.CreateDirectory(directoryName);
                if (fileName != String.Empty)
                {
                    //解压文件到指定的目录 
                    FileStream streamWriter = File.Create(path + theEntry.Name);
                    int size = 2048;
                    byte[] data = new byte[2048];
                    while (true)
                    {
                        size = s.Read(data, 0, data.Length);
                        if (size > 0)
                        {
                            streamWriter.Write(data, 0, size);
                        }
                        else
                        {
                            break;
                        }
                    }
                    streamWriter.Close()；
                }        
            }
            s.Close();
        }
        public void ZipFile(string FileToZip, string ZipedFile, int CompressionLevel, int BlockSize)
        {
            //如果文件没有找到，则报错 
            if (!System.IO.File.Exists(FileToZip))
            {
                throw new System.IO.FileNotFoundException("The specified file " + FileToZip + " could not be found. Zipping aborderd");
            }
            System.IO.FileStream StreamToZip = new System.IO.FileStream(FileToZip, System.IO.FileMode.Open, System.IO.FileAccess.Read);
            System.IO.FileStream ZipFile = System.IO.File.Create(ZipedFile);
            ZipOutputStream ZipStream = new ZipOutputStream(ZipFile);
            ZipEntry ZipEntry = new ZipEntry("ZippedFile");
            ZipStream.PutNextEntry(ZipEntry);
            ZipStream.SetLevel(CompressionLevel);
            byte[] buffer = new byte[BlockSize];
            System.Int32 size = StreamToZip.Read(buffer, 0, buffer.Length);
            ZipStream.Write(buffer, 0, size);
            try
            {
                while (size < StreamToZip.Length)
                {
                    int sizeRead = StreamToZip.Read(buffer, 0, buffer.Length);
                    ZipStream.Write(buffer, 0, sizeRead);
                    size += sizeRead;
                }
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
            ZipStream.Finish();
            ZipStream.Close();
            StreamToZip.Close();
        }
        /// <summary>
        /// 压缩
        /// </summary>
        /// <param name="args"></param>
        public void ZipFileMain(string[] args)
        {
            string a = Directory.GetFiles(args[0]).ToString();
            string[] filenames = Directory.GetFiles(args[0]);
            Crc32 crc = new Crc32();
            ZipOutputStream s = new ZipOutputStream(File.Create(args[1]));
            s.SetLevel(6); // 0 - store only to 9 - means best compression 
            foreach (string file in filenames)
            {
                //打开压缩文件 
                FileStream fs = File.OpenRead(file);
                byte[] buffer = new byte[fs.Length];
                fs.Read(buffer, 0, buffer.Length);
                ZipEntry entry = new ZipEntry(file);
                entry.DateTime = DateTime.Now;
                // set Size and the crc, because the information 
                // about the size and crc should be stored in the header 
                // if it is not set it is automatically written in the footer. 
                // (in this case size == crc == -1 in the header) 
                // Some ZIP programs have problems with zip files that don't store 
                // the size and crc in the header. 
                entry.Size = fs.Length;
                fs.Close();
                crc.Reset();
                crc.Update(buffer);
                entry.Crc = crc.Value;
                s.PutNextEntry(entry);
                s.Write(buffer, 0, buffer.Length);
            }
            s.Finish();
            s.Close();
        } 
     }
}
问题是我自己生成的ZIP 压缩文件可以解压，但是我下载下来的ZIP 却不能解压，很是郁闷 ，而且自己生成压缩文件也不是用这些代码生成的，是另外写的代码、、、望高手指点