error in populating dropdownlist

See more:

system

drop-down

mail

i received this error when populating the dropdownlist. any suggestion pls?

System.Web.UI.WebControls.DropDownList

the scenario is, a user is sending information from a c# page and will send it to the email provided.

heres the code:

protected void btnSubmit_Click(object sender, EventArgs e)
{
    try
    {
        MailMessage Msg = new MailMessage();
        Msg.From = txtEmail.Text;
        Msg.To = txtTo.Text;
        Msg.Subject = txtSubject.Text;
        Msg.Body = "Name:" + txtFrom.Text + "Department:" + drpDep.Text;

        SmtpMail.SmtpServer = "mail.domain.com";
        SmtpMail.Send(Msg);
        Msg = null;
        //Page.RegisterStartupScript("UserMsg", "<script>alert('Mail sent thank you...');if(alert){ window.location='/ETC/';}</script>");
        Response.Redirect("../Confirmation.aspx");
    }
    catch (Exception ex)
    {
        Console.WriteLine("{0} Exception caught.", ex);
    }
}