datalist 折叠 当前上下文中不存在名称

前台代码:
<asp:DataList ID="ddlone" runat="server" OnItemDataBound="ddlone_ItemDataBound"  >
               <HeaderTemplate>
                 <table>
                      <thead>
                             <td>操作</td>
                             <td >名称</td>
                        </thead>
                </HeaderTemplate>
                <ItemTemplate>
                     <tr >
                        <td align="left">
                         <img src="" alt="open" onclick="expand('<%#Eval("child_id") %>')" />
                         </td>
                         <td align="left" ><%#Eval("name") %>
                         </td>
                     </tr>
                     <tr id="<%#Eval("child_id") %>">
                         <td colspan="3">
                             <asp:DataList ID="ddltwo" runat="server">
                                <ItemTemplate>
                                    <tr>
                                     <td align="left">
                                         <img src="" alt="close"/>
                                     </td>
                                     <td align="left">
                                         <%#Eval("name") %>                                         
                                     </td>                                         
                                     </tr>                                 
                                 </ItemTemplate>
                           </asp:DataList>
                         </td>
                   </tr>
                 </ItemTemplate>
                 <FooterTemplate> 
                    </table>
                 </FooterTemplate>
             </asp:DataList>
cs:    protected void ddlOne_ItemDataBound(object sender, EventArgs e)
    {
        
        string strTwo = "select child_id,name from aa where parent_id='2' and child_id is not null order by id asc";
        ddlTwo.DataSource = DBHelp.ExecuteDataSet(strConn, strTwo).Tables[0].DefaultView;
        ddlTwo.DataBind();
    }
js:function expand(id)    
{    if(document.getElementById(id).style.display=='none')    
     {document.getElementById(id).style.display='block';   
      }    
else    
    {
    document.getElementById(id).style.display='none';        }  
  }错误信息:当前上下文中不存在名称“ddlTwo”