Use of Detailview with drop down list in asp.net 2.0

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
rebindStudentRecord();
FillStudentRecord();
}
}

public void rebindStudentRecord()
{
con = new SqlConnection(ConfigurationManager.AppSettings["ConnectionString"]);
cmd.CommandText = "Select * from UserRecord";
cmd.Connection = con;
ds = new DataSet();
da = new SqlDataAdapter(cmd);
con.Open();
cmd.ExecuteNonQuery();
da.Fill(ds);
con.Close();
ddlStudent.DataValueField = "UserId";
ddlStudent.DataTextField = "UserId";
ddlStudent.DataSource = ds;
ddlStudent.DataBind();
ddlStudent.Items.Add("Select User ID");
ddlStudent.Items.FindByValue("Select User ID").Selected = true;
}

protected void ddlStudent_SelectedIndexChanged(object sender, EventArgs e)
{
if (ddlStudent.SelectedValue.ToString() == "Select User ID")
{
lblError.Visible = true;
lblError.Text = "Select User ID To See Student record";
DetailsViewStudentRecord.DataSource = null;
DetailsViewStudentRecord.DataBind();
}
else
{
FillStudentRecord();
}
}

public void FillStudentRecord()
{
if (ddlStudent.SelectedValue.ToString() == "Select User ID")
{
lblError.Visible = true;
lblError.Text = "Select User ID To See Student record";
}
else
{
string StudentUserID = ddlStudent.SelectedValue.ToString();
con = new SqlConnection(ConfigurationManager.AppSettings["ConnectionString"]);
cmd.CommandText = "Select * from UserRecord Where UserId= '" + StudentUserID + "'";
cmd.Connection = con;
da = new SqlDataAdapter(cmd);
ds = new DataSet();
con.Open();
cmd.ExecuteNonQuery();
da.Fill(ds);
con.Close();

if (ds.Tables[0].Rows.Count > 0)
{
DetailsViewStudentRecord.DataSource = ds;
DetailsViewStudentRecord.DataBind();
lblError.Visible = false;
}
else
{
lblError.Visible = true;
lblError.Text = "No Record Exist To This User ID";
DetailsViewStudentRecord.DataSource = null;
DetailsViewStudentRecord.DataBind();
}
}
}
}

Web.config: