“Illegal Choice has been detected”
If you don't want to validate that field, then remove the following function

function test_mail1_validate($form, &amp;$form_state) {



  if (!(is_numeric($form_state['input']['field_abc']))) {

    form_set_error('field_abc','ERROR');

  }
}


And remove the following line from test_mail1_form

$form['#validate'][] = 'test_mail1_validate';