Error:'drpEmpCode' has a SelectedValue which is invalid because it does not exist in the list of ite [Resolved]

protected void Button1_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection("Data Source=.\\SQLEXPRESS;AttachDbFilename=E:\\vip\\BVIS\\BVIS\\App_Data\\VehicleDb.mdf;Integrated Security=True;User Instance=True");
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
con.Open();
cmd.CommandText = "select * from tblalloc where VNo='" + drpVno.Text.Trim() + "'";
SqlDataReader rdr = cmd.ExecuteReader();
//rdr = cmd.ExecuteReader();
bool temp = false;
while (rdr.Read())
{
drpVno.Text = rdr.GetValue(0).ToString();
drpEmpCode.Text = rdr.GetString(2);
drpDrCode.Text = rdr.GetString(1);
drpBrCode.Text = rdr.GetString(3);
drpPrps.Text = rdr.GetString(4);
temp = true;
}
if (temp == false)
{

string tmp = "";
tmp = "<script language='javascript'>";
tmp += "alert('Vehicle No. not found');";
tmp += "</script>";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "MyScript", tmp);

}

what is the problem with the code?

[Resolved]