为什么老是出现“未将对象引用设置到对象的实例”

能说清楚点吗 哪个地方要加new啊 单独的上传程序 我以前都没加过new啊

我的上传控件是html组件中的file filed 将他转化为服务器控件运行 代码如下：

    HttpPostedFile hpf=F.PostedFile;
                        int cl=hpf.FileName.Length;
                        
                        if(cl>0)
                        {
                            if(hpf.FileName=="")
                            {
            
                                RegisterStartupScript("","<script>alert('你上传的文件不能为空！')</script>");

                            }
                            else
                            {
                                string kuo=Path.GetExtension(hpf.FileName).ToLower();
                                if(kuo==".jpg" || kuo==".gif" || kuo==".bmp" )
                                {
                
                                    if(hpf.ContentLength<660000)
                                    {
                                        filename=DateTime.Now.ToString("yyyMMdd")+Path.GetFileName(hpf.FileName);
                                        string filepath=Server.MapPath("loadfile/");
                                        hpf.SaveAs(filepath+filename);

                                    }
                                    else
                                    {
                                        RegisterStartupScript("","<script>alert('请将你所上传的文件控制在600kb内！')</script>");
                                    }
                                }
                                else
                                {
                                    RegisterStartupScript("","<script>alert('上传图片的格式要为jpg,gif,bmp！')</script>");
                                }
                            }
                        }
                        else
                        {
                            filename=face;
                        }


                        conndb cdb=new conndb();
                        int i=cdb.reg(xm,mm,filename,xb,qm,yx,wt,da,lz);
                        FormsAuthentication.SetAuthCookie(i.ToString(),false);