Meta Tag: The Controls collection cannot be modified because the control contains code blocks

Hi every one 

i want use meta tag in my page that read keyword from database

i set this code in my product.aspx page 

 protected void Page_Load(object sender, EventArgs e)
    {
        SqlCommand _cmd = new SqlCommand("select Keyword1 + ',' + Keyword2 + ',' +Keyword3 from House_info where BehCode=1115", _cn);

        _cn.Open();
        SqlDataReader _dr = _cmd.ExecuteReader();
        while (_dr.Read())
        {

            HtmlMeta htmlMeta;
           
            string keyword = _dr[0].ToString();


            htmlMeta = new HtmlMeta();
            htmlMeta.HttpEquiv = "keywords";
            htmlMeta.Content = keyword;
            this.Page.Header.Controls.Add(htmlMeta);
        }
    }

it worked correctly and show my keywords from database and show it in my product.aspx metatag

i have two other page

index.aspx   and store.aspx  in index.aspx i have 1button and 1 TextBox when user type their BEHCODE(columns name in users table) in TextBox it go to store.aspx page and show that users information on store.aspx

Now i want set meta tag in store.aspx page and i want  fill store.aspx  meta tag from my users table in data base

this is index.aspx

    protected void ImageButton3_Click(object sender, ImageClickEventArgs e)
    {

        string data = Server.UrlEncode(txtNumeric.Text);

        SqlCommand _cmd = new SqlCommand("traidname", _cn);
        _cmd.CommandType = CommandType.StoredProcedure;

        _cmd.Parameters.Add("@BehCode", data);

        _cn.Open();
        string tName = _cmd.ExecuteScalar().ToString();

        _cn.Close();
        Response.Redirect(tName + "?BehCode=" + Server.UrlEncode(txtNumeric.Text));

and store.aspx behind code

  SqlCommand _cmd = new SqlCommand("storeInfo", _cn);
        _cmd.CommandType = CommandType.StoredProcedure;
        _cmd.Parameters.AddWithValue("@BehCode",data);
        _cn.Open();
        SqlDataReader _dr = _cmd.ExecuteReader();
        while (_dr.Read())
        {


            HtmlMeta htmlMeta;

            string keyword = _dr[0].ToString();


            htmlMeta = new HtmlMeta();
            htmlMeta.HttpEquiv = "keywords";
            htmlMeta.Content = keyword;
            this.Page.Header.Controls.Add(htmlMeta);


            Lblbehcode.Text = _dr["Name"].ToString();
            Image1.ImageUrl = "~/image/behcode/" + _dr["Image_Behcode"].ToString();

here when i run website this error occur

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

in this line

this.Page.Header.Controls.Add(htmlMeta);

i use this code too 

<script type="text/javascript">

        $("input[id$=btnButton]").live("click", function () {

            return confirm("Do you want to submit?");

        });

    </script>

but it didn't worked this problem just happen here when i used  meta tag code in  other page it worked correctly .

why this happen?

thanks