How to work on SQL Subqueries with OleDbDataReader?

[Meng]

Whenever I run the code, I get an exception "No value given for one or more required parameters". I don't find anything wrong with the SQL statement (or are there any?). Basically I'm trying to get the user input and look for the corresponding CourseNumber then match the CourseNumber and TopicNumber. Then I will look up for the TopicName using TopicNumber.

   protected void AddAssignment()
        {
            OleDbConnection conn = null;
            OleDbDataReader reader;
            try
            {
                conn = new OleDbConnection("Provider=Microsoft.Jet.OleDB.4.0;" + "Data Source=" + Server.MapPath("~/Data/RPMH.mdb"));
 
                conn.Open();
 
                OleDbCommand cmd = new OleDbCommand("SELECT TopicName FROM Topic WHERE TopicNumber IN (SELECT TopicNumber FROM CourseTopic WHERE CourseNumber = (SELECT CourseNumber FROM Course WHERE CourseName ='"+AddClass.courseselect+"'))", conn);
 
                TopicList.DataValueField = "Topic";
                TopicList.DataTextField = "Topic";
 
               while (reader.Read())
                {
                    ListItem newItem = new ListItem();
                    newItem.Value = (string)reader["TopicName"];
                    newItem.Text = (string)reader["TopicName"];
                    TopicList.Items.Add(newItem);
                }
                reader.Close();
            }
            finally
            {
                if (conn != null)
                    conn.Close();
            }
        }