Don't close  the DataReader until you have
bound the controls:

private void BindListBox(DropDownList listControl, string Sql, string dataText,
string dataValue, string listText)

OleDbDataReader dr;

dr = DBUtility.GetDataReader(Sql);

if(dr != null)

{

if(dr.FieldCount > 0)

{

listControl.DataSource = dr;

listControl.DataTextField = dataText;

listControl.DataValueField = dataValue;

listControl.DataBind();

listControl.Items.Insert(0, listText);

listControl.SelectedIndex = 0;

}

}

dr.Close();

}

To get DataReader:

public static OleDbDataReader GetDataReader(string SQLString)

{

OleDbConnection cn = new OleDbConnection(DBConnString);

OleDbDataReader dr;

try

{

cn.Open();

OleDbCommand cmd = cn.CreateCommand();

cmd.CommandText = SQLString;

dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);

}

catch (Exception e)

{

throw e;

}

return dr;

}

Also when you open the datareader, set the param to
CommandBehavior.CloseConnection eg:

(VB code):

myDataReader = myCommand.ExecuteReader(CommandBehavior.CloseConnection)

This will close  the connection  when you close the datareader.

public void RunProc(string procName, out SqlDataReader dataReader)
{
SqlCommand cmd = CreateCommand(procName, null);
dataReader = cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
}

public SqlDataReader GetList(string prodid)
{
SqlDataReader dataReader = null;
try
{
// create data  object and params
Database data = new Database();
SqlParameter[] prams = { data.MakeInParam("@prodid", SqlDbType.VarChar, 30,
prodid) };

// run the stored procedure
data.RunProc("Get_List_sp", prams, out dataReader);
}
catch (Exception ex)
{
Error.Log(ex.ToString());
}

return dataReader;
}dataReader;
}

SqlDataReader reader = null;
string prodid = Request.QueryString["product_id"];
reader = GetList(prodid);
..... bind controls

there's bits missing from that, make a global var private
SqlConnection con; to the class

private void Open()
{
con = new SqlConnection("server=" + server + ";database=" + db + ";User Id=" +
user + ";password=" + pass);
//..........different ways to do this ia web.config, global.asax etc
}

private SqlCommand CreateCommand(string procName, SqlParameter[] prams)
{
SqlCommand cmd = null;
// make sure connection  is open
Open();

cmd = new SqlCommand(procName, con);
cmd.CommandType = CommandType.StoredProcedure;

// add proc parameters
if (prams != null)
{
foreach (SqlParameter parameter in prams)
cmd.Parameters.Add(parameter);
}

// return  param
cmd.Parameters.Add(
new SqlParameter("ReturnValue", SqlDbType.Int, 4,
ParameterDirection.ReturnValue, false, 0, 0,
string.Empty, DataRowVersion.Default, null));

return cmd;
}

/// <summary>
/// close  the connection.
/// </summary>
public void Close()
{
if (con != null)
con.Close();
}

/// <summary>
/// Release resources.
/// </summary>
public void Dispose()
{
// make sure connection is closed
if (con != null)
{
con.Dispose();
con = null;
}
}

//Note execute nonquery requires you to close()

public int RunProc(string procName)
{
SqlCommand cmd = CreateCommand(procName, null);
cmd.ExecuteNonQuery();
this.Close();
return (int)cmd.Parameters["ReturnValue"].Value;
}