i am trying to fetch customer address from database on selec

here is my code:

private void cmbCustomer_SelectedIndexChanged(object sender, EventArgs e)

{

//id = Convert.ToInt64(cmbCustomer.SelectedValue);

DataSet ds = new DataSet();

SqlCommand cmd = new SqlCommand("select * from RM_Customer where custID ='" +Convert.ToInt64(cmbCustomer.SelectedValue) + "'", cn);

cn.Close();

cn.Open();

SqlDataReader dr = cmd.ExecuteReader();

if (dr.Read())

{

txtaddress.Text = dr["custAddress"].ToString();

}

dr.Close();

cn.Close();

}

i got error like this:

Unable to cast object of type 'System.Data.DataRowView' to type 'System.IConvertible'