Drupal 7 Forms API - AJAX Forms error: An illegal choice has been detected. Please contact the site administrator

Question

I have a form set up where a users selects an item from a drop down. Once that item is selected another drop down is populated. Then depending on the value that is selected from the second drop down a fieldset may or may not be shown. If the field set is shown there is a field and a button. By clicking the button you add another copy of the same field. Once there is more than one a remove one button shows up as well. I got the basis for the code from here: http://api.drupal.org/api/examples/ajax_example%21ajax_example_graceful_degradation.inc/function/ajax_example_add_more/7

The problem is when I click 'Add Another Survey Question' the first time it works fine and add a field. When I click it a second time or when I click remove now that there are two, I get this error: 'An illegal choice has been detected. Please contact the site administrator.'

What am I doing wrong?

Here's my code:

function touchpoints_addmetric_form($form, &$form_state, $tp_id) {
    $selectedType = isset($form_state['values']['type']) ? $form_state['values']['type'] : FALSE;
    $types = db_query('SELECT * FROM {touchpoints_metric_types}') -> fetchAllKeyed(0, 1);
    $form['#tree'] = TRUE;
    $form['type'] = array(
        '#type' => 'select',
        '#title' => t('Metric Type'),
        '#options' => $types,
        '#required'=>TRUE,
        '#ajax' => array(
            'event' => 'change',
            'wrapper' => 'method-wrapper',
            'callback' => 'touchpoints_method_callback'
        )
    );
    $form['measurementmethod'] = array(
        '#type' => 'select',
        '#title' => t('Measurement Method'),
        '#required'=>TRUE,
        '#prefix' => '<div id="method-wrapper">',
        '#suffix' => '</div>',
        '#options' => _get_methods($selectedType)
    );
    $form['survey'] = array('
        #type' => 'fieldset',
        '#collapsible' => FALSE,
        '#states' => array(
            'visible' => array(
                array(
                    array(':input[name="measurementmethod"]' => array('value' => '5')), 
                    'xor', 
                    array(':input[name="measurementmethod"]' => array('value' => '6')),
                    'xor', 
                    array(':input[name="measurementmethod"]' => array('value' => '7'))
                )
            )
        )
    );
    $form['survey']['contents'] = array(
        '#type' => 'fieldset',
        '#collapsible' => FALSE,
        '#prefix' => '<div id="survey-div">', 
        '#suffix' => '</div>', 
    );
    if (empty($form_state['num_surveys'])) {
        $form_state['num_surveys'] = 1;
    }
    for ($i = 1; $i <= $form_state['num_surveys']; $i++) {
        $form['survey']['contents']['survey_question'][$i] = array(
            '#type' => 'textfield',
            '#title' => t('Survey Question ' . $i),
            '#size' => 70, '#maxlength' => 100, 
        );
    }
    $form['survey']['contents']['addsurvey'] = array(
        '#type' => 'submit',
        '#value' => t('Add Another Survey Question'),
        '#submit' => array('touchpoints_metrics_survey_add_one'),
        '#limit_validation_errors' => array(),
        '#ajax' => array(
            'callback' => 'touchpoints_metrics_survey_callback', 
            'wrapper' => 'survey-div', 
        ), 
    );
    if ($form_state['num_surveys'] > 1) {
        $form['survey']['contents']['removesurvey'] = array(
            '#type' => 'submit',
            '#value' => t('Remove A Survey Question'),
            '#submit' => array('touchpoints_metrics_survey_remove_one'), 
            '#limit_validation_errors' => array(), 
            '#ajax' => array(
                'callback' => 'touchpoints_metrics_survey_callback', 
                'wrapper' => 'survey-div', 
            ), 
        );
    }
    return $form;
}

function _get_methods($selected) {
    if ($selected) {
        $methods = db_query("SELECT * FROM {touchpoints_m_methods} WHERE mt_id=$selected") -> fetchAllKeyed(0, 2);
    } else {
        $methods = array();
    }
    return $methods;
}

function touchpoints_method_callback($form, &$form_state) {
    return $form['measurementmethod'];
}

function touchpoints_metrics_survey_add_one($form, &$form_state) {
    $form_state['num_surveys']++;
    $form_state['rebuild'] = TRUE;
}

function touchpoints_metrics_survey_remove_one($form, &$form_state) {
    if ($form_state['num_surveys'] > 1) {
        $form_state['num_surveys']--;
    }
    $form_state['rebuild'] = TRUE;
}

function touchpoints_metrics_survey_callback($form, &$form_state) {
    return $form['survey']['contents'];
}

Answer 1

Actually, it's '#validated' => TRUE.

Answer 2

I have encountered this error a few times, and this is what I found:

This is Drupal's way of saying "Hey, you tried to submit this form with a , checkbox or radio button option that wasn't included in the original form definition! That's not allowed." - See more at: http://proofgroup.com/blog/2008/jul/debugging_mysterious_illegal_choice_has_been_detected_please_contact_site_administrato#sthash.vDNmqslL.dpuf

Instead of custom code, maybe you should consider module Conditional Fields

Or a work around: '#validate' => TRUE source