无法在asp .net中下载文件

using System;
using System.IO;
using System.Web;

public class DownloadFile : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        string filePath = "path_to_your_file"; // 文件路径
        string fileName = Path.GetFileName(filePath); // 文件名
        string fileType = "application/octet-stream"; // 文件类型

        context.Response.Clear();
        context.Response.ContentType = fileType;
        context.Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName);
        context.Response.AddHeader("Content-Length", new FileInfo(filePath).Length.ToString());

        using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
        {
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                context.Response.OutputStream.Write(buffer, 0, bytesRead);
                context.Response.Flush();
            }
        }

        context.Response.End();
    }

    public bool IsReusable
    {
        get { return false; }
    }
}

<configuration>
  <system.webServer>
    <handlers>
      <add name="DownloadFileHandler" path="DownloadFile.ashx" verb="GET" type="DownloadFile" resourceType="Unspecified" preCondition="integratedMode" />
    </handlers>
  </system.webServer>
</configuration>