Dropdown results in Empty = "Enumeration yielded no results"

hello, i have been try to retrieve the data from the database, but it results in Empty = "Enumeration yielded no results" any solutions. here is my code,

 

public void DiametrDropDown()

{

// string CS = ConfigurationManager.ConnectionStrings[""].ConnectionString;

// string data = "select PHYSICAL_ID,SUBSTRING(MODEL,6,len(MODEL)) as Model from PHYSICAL_DATA_PSYCHOLMETRICS as P";

SqlCommand cmd = new SqlCommand("select PHYSICAL_ID,SUBSTRING(MODEL,6,len(MODEL)) as Model from PHYSICAL_DATA_PSYCHOLMETRICS as P", conn);

conn.Open();

DDLDiameter.DataSource = cmd.ExecuteReader();// where the result from the query is assigned to the dropdown id

DDLDiameter.DataTextField = "Model";

DDLDiameter.DataValueField = "PHYSICAL_ID";

DDLDiameter.DataBind();

conn.Close();

}