How to make a checkbox readonly inside a GridView if the value is a certain number

I have the following asp.net checkbox inside a GridView which is inside an UpdatePanel:

<asp:UpdatePanel ID="upSubasks" ClientIDMode="Static" runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <div id="dvSubtasksHolder" runat="server" style="width: 98%;" class="brClear padTop">
            <asp:GridView ShowHeaderWhenEmpty="false" ID="gvSubTasks" runat="server" AutoGenerateColumns="false">
                <Columns>
                    <asp:BoundField DataField="Subtask ID" HeaderText="Subtask ID" HeaderStyle-CssClass="hideTag" ItemStyle-CssClass="hideTag" />
                    <asp:TemplateField HeaderText="Complete">
                        <ItemTemplate>
                            <asp:CheckBox ID="cbIsComplete" runat="server" AutoPostBack="true" Enabled='<%# Eval("Complete Subtask").ToString() == "1" ? false : true %>' Checked='<%# Eval("Complete Subtask").ToString() == "1" ? true : false %>' OnCheckedChanged="cbIsComplete_CheckChanged" />
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>
        </div>
    </ContentTemplate>
</asp:UpdatePanel>

code-behind:

protected void cbIsComplete_CheckChanged(object sender, EventArgs e)
{
    string cText = ((GridViewRow)(((System.Web.UI.WebControls.CheckBox)sender).Parent.Parent)).Cells[0].Text;
    int selRowIndex = ((GridViewRow)(((System.Web.UI.WebControls.CheckBox)sender).Parent.Parent)).RowIndex;
    System.Web.UI.WebControls.CheckBox cb = (System.Web.UI.WebControls.CheckBox)gvSubTasks.Rows[selRowIndex].FindControl("cbIsComplete");

    using (SqlConnection oCon = new SqlConnection(gloString))
    {
        using (SqlCommand qSave = new SqlCommand())
        {
            qSave.Connection = oCon;
            qSave.CommandType = CommandType.Text;
            qSave.CommandText = @""; //update command

            try
            {
                oCon.Open();
                qSave.ExecuteNonQuery();
            }
            catch (SqlException ce)
            {
            }
            finally
            {
                oCon.Close();
            }
        }
    }

    upSubasks.Update();
}

What I am looking to do is when the upSubtasks.Update() executes the checkbox to be disabled in "checked" state (the value is 1) but that is not happening. I can uncheck the checkbox once the UpdatePanel does the updating.