ASP.Net controls

Am populating a combobox using a class, Now the weird thing the name of the combobox cannot be found in the code behind and every thing was working fine till now.

Yes Sir by "name" I mean "ID"
//A method in code behind
public void populateCombo()
{
DataCls dtClass = new DataCls();

cboCourses.DataSource = dtClass.CognosComboBox();
cboCourses.DataBind();

}

// Below is My form

<asp:Content ID="Content1" ContentPlaceHolderID="sideContent" Runat="Server">
 <div class="entry">
<p>Register <a href="Register.aspx">HERE</a> if you not a member.</p>

<table border="0">
<tr>
<td> Choose course:</td>
<td>
<asp:DropDownList ID="cboCourses" runat="server">
</asp:DropDownList>
</td>

</tr>
<tr>
<tr><td colspan="2" align="center">
<asp:Button ID="btnEnroll" runat="server"
Text="submit" onclick="btnEnroll_Click" /></td></tr>


</table>

</div>
</asp:Content>

//Below is the code in my method

public ArrayList CognosComboBox()
{
dbConnection();

string sqlCBO = "SELECT courseName FROM Courses;";
dbCmd = new OleDbCommand(sqlCBO, dbConn);

OleDbDataReader reader = dbCmd.ExecuteReader();

ArrayList myList = new ArrayList();
myList.Add("Choose course");
while (reader.Read())
{
myList.Add(reader[0].ToString());
}
reader.Close();


dbConn.Close();

return myList;

}

Sorry Arry List Methos runs in my class