登录界面跳到后台管理界面时，一级菜单跳到子菜单时会报错

  <table width="868px" border="0" cellspacing="0" cellpadding="0"><tr style="background-color:#E0E0E0">     <% 
         string loadPage = "";//首页
         
         
         string MenuID = new Maticsoft.BLL.school.vn_sys_Oprator().GetModel(Convert.ToInt32(Session["UserID"].ToString())).MenuID;  //     异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。  
         System.Data.DataTable dt1 = new Maticsoft.BLL.school.vn_sys_Oprator().GetList(" ParentId=0").Tables[0];
         if (dt1.Rows.Count > 0)
         {
             for (int j = 0; j < dt1.Rows.Count; j++)
             {
                 if (MenuID.IndexOf("," + dt1.Rows[j]["id"].ToString() + ",") > -1)
                 {
                                              loadPage = dt1.Rows[0]["PagePath"].ToString() + "?id=" + dt1.Rows[0]["ID"].ToString();
                     
                     
                     
                     
     %>
      
        <td style="height: 16px"><a href="<%=dt1.Rows[j]["PagePath"].ToString() %>?id=<%=dt1.Rows[j]["ID"].ToString() %>" target="center" class="fei2"><%=dt1.Rows[j]["MenuName"].ToString() %></a></td>
      
      <%
      }
             }
         } 
      %>
      
      
      <td style="height: 16px">
          </td>
     
         
    </tr></table>