Error converting data type nvarchar to float
<p>I am getting the following error in my code.</p>

<blockquote>
  <p>Error converting data type nvarchar to float.</p>
</blockquote>

<p>My code on button click is </p>

<pre><code> protected void btnFind_Click(object sender, EventArgs e)
    {

        SqlParameter LatParam;
        SqlParameter LngParam;


    if (zipcode.Text != "")
    {
        litAddress.Text = "";
        litAddress1.Text = "";
        string addressstring = zipcode.Text;


        string connstring = "Data Source=win2008-2;Initial Catalog=h1tm11;User ID=sa;Password=#1cub3123*;Persist Security Info=True;";


        string SQL1 = "SELECT *, 6371.01 * ACOS( SIN( @lat*PI()/180 ) * SIN( store_lat*PI()/180 ) + COS( @lat*PI()/180 ) * COS( store_lat*PI()/180 ) * COS( (store_long*PI()/180) - (@lng*PI()/180) ) ) AS distance from storelocator where 6371.01 * ACOS( SIN( @lat*PI()/180 ) * SIN( store_lat*PI()/180 ) + COS( @lng*PI()/180 ) * COS( store_lat*PI()/180 ) * COS( (store_long*PI()/180) - (@lng*PI()/180) ) ) &lt; '" + ddl_distance.SelectedItem.Value + "' order by distance asc;";

        SqlConnection conn = new SqlConnection(connstring);

        conn.Open();
        SqlCommand comm = new SqlCommand(SQL1, conn);
        LatParam = new SqlParameter();
        LatParam.ParameterName = "@lat";
        LatParam.SqlDbType = SqlDbType.NVarChar;
        LatParam.Value =  "select lat from tbl_pincode where codes='" + zipcode.Text + "';";

        LngParam = new SqlParameter();
        LngParam.ParameterName = "@lng";
        LngParam.SqlDbType = SqlDbType.NVarChar;
        LngParam.Value ="select lat from tbl_pincode where  codes='" + zipcode.Text + "';";



        comm.Parameters.Add(LatParam);
        comm.Parameters.Add(LngParam);





        SqlDataReader reader = comm.ExecuteReader(CommandBehavior.CloseConnection);


            while (reader.Read())
            {
                string area = reader["lat"].ToString();
                string codes =reader["lng"].ToString();



                litAddress.Text += area;
                litAddress1.Text += codes;




            }



    }
</code></pre>

<p>The datatype in the table are nvarchar for latitude,longitude and pincodes.</p>

<p>Thanks,</p>
