问导出文件到客户端下载后，页面左下角出现异常提示，然后页面按钮点击就没有效果，重新打开页面 ，恢复正常

System.Text.StringBuilder outputBuffer=new System.Text.StringBuilder();string filename=DateTime.Now.ToString("yyyyMMddhhmmss")+".txt";outputBuffer.AppendFormat("{0}",savetxt);System.Web.HttpContext.Current.Response.Clear();System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename="+filename);//System.Web.HttpContext.Current.Response.AddHeader("Content-Length", size);System.Web.HttpContext.Current.Response.ContentType = "application/octet-stream";    System.Web.HttpContext.Current.Response.Charset = "UTF-8";System.Web.HttpContext.Current.Response.BinaryWrite(System.Text.Encoding.UTF8.GetBytes(outputBuffer.ToString()));System.Web.HttpContext.Current.Response.End();