Это может работать:
SqlConnection con = new SqlConnection("Data Source=192.168.1.12;Initial Catalog=Ibrahim;User ID=sa;Password=1412;");
con.Open();
SqlCommand cmd = new SqlCommand("insert into Ibrahim.EVC_Activation_Val (Date,Dealer,Transaction_ID,Invoice_ID,Mobile_Num,Quantity_LE) values('" + DateTimePicker1.Value.ToString("yyyy/mm/dd") + "','" + Txtbx1.Text + "','" + Txtbx2.Text + "','" + Txtbx3.Text + "','" + Txtbx4.Text + "','" + Txtbx5.Text + "')",con);
cmd.ExecuteNonQuery();
MessageBox.Show("Saved");
con.Close();