为什么登陆页面输入相关信息后总是显示“查无此人”呢？高手帮忙。。。谢谢

为什么登陆页面输入相关信息后总是显示“查无此人”呢？
麻烦高手看下一下代码 那里错了
 string adminName = txtadmin.Text;
                string adminpwd = txtpwd.Text;
               
                if(AdminInfoBus.selectadmin(adminName,adminpwd)!=null)
                {
                SqlCommand cmd = new SqlCommand("select adminpwd from adminInfo where  adminName=" + this.txtadmin.Text, con);//User是自己创建的一个表
                try
                {
                    string adminPwd = cmd.ExecuteScalar().ToString();  //如果没有查到密码，转换会有异常
                    if (adminPwd != this.txtpwd.Text)  //判断密码是否正确
                    {
                        Response.Write("<script>alert('密码不正确！')</script>");
                    }
                    else
                    {
                        //密码正确，页面转向
                        Response.Redirect("WebForm1.aspx");
                    }
                }
                catch
                {
                    Response.Write("<script>alert('查无此人！')</script>");
                }
                finally
                {
                    con.Close();  //关闭连接
                }
                }
           
                else
                { Response.Write("<script>alert('用户名或密码错误！');</script>");
                }