C# - Accessing Data From Sql In Two Dropdown List At Same Time

i have two drop down list in web form..for both of them i've used following code to bind with sql..but whenever i'm trying to bind second drop down list with same method..it's giving error..
the code i've used:

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
ddlPropertyType.AppendDataBoundItems = true;
String strConnString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
String strQuery = "select ID, PropertyName from PropertyType";
SqlConnection con = new SqlConnection(strConnString);
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = strQuery;
cmd.Connection = con;
try
{
con.Open();
ddlPropertyType.DataSource = cmd.ExecuteReader();
ddlPropertyType.DataTextField = "PropertyName";
ddlPropertyType.DataValueField = "ID";
ddlPropertyType.DataBind();
}
catch (Exception ex)
{
throw ex;
}
finally
{
con.Close();
con.Dispose();
}
}
}