When Updating error occurs

when i inserting a radio button error occurs please help me.Code as follows;

private void button1_Click(object sender, EventArgs e)

{

con.Open();

SqlCommand cmd2 = new SqlCommand("Update diesel set Billno = '" + cb_billno.Text + "',Date = '" + dateTimePicker1.Text + "',Dieselcost = " + textBox1.Text + ",Dieselservice=" + txt_dieselservice.Text + ",Servicetax= " + txt_servicetax.Text + ",Educess = " + txt_educess.Text + ",Addcess = " + txt_addcess.Text + ",Sertax= " + txt_sertaxtot.Text + ",Totbill= " + txt_totbillvalue.Text + " ,Flag='" + radioButton1.Text+"','" + radioButton2.Text+"' where SNO = " + cb_sno.Text + "", con);

cmd2.ExecuteNonQuery();

con.cose();

}