Checkbox does not work

<asp:Repeater ID="rptrrol" runat="server" OnItemDataBound="rptrrol_ItemDataBound">
                   <ItemTemplate>

                       <dl>
                           <dt>

                               <button id="btn"  runat="server">+</button><asp:CheckBox ID="chkrole" runat="server" CssClass="topic" Text='<%#Eval("role") %>' ValidationGroup="user" AutoPostBack="true" Checked='<%# Eval("role")%>' />

                               <asp:Repeater ID="rptrsubrole" runat="server">
                                   <ItemTemplate>
                                       <dd style="margin-removed 10px;">
                                           <asp:CheckBox ID="chksubrole" runat="server" Text='<%#Eval("role") %>' ValidationGroup="user" />
                                           <br />

                                       </dd>
                                   </ItemTemplate>
                               </asp:Repeater>
                           </dt>
                       </dl>

                   </ItemTemplate>
               </asp:Repeater>

protected void btnsave_Click(object sender, EventArgs e)
{
 foreach (RepeaterItem item in rptrrol.Items)
        {
            CheckBox ch = item.FindControl("chkrole") as CheckBox;

            if (ch != null && ch.Checked == true)
            {
                ch.Text = "IT is selected now";
            }
        }
}