Validate correct number of columns in each rows

To create empty cell, you may use syntax like "1|2|3||4"

add to cck_table.module:

<?php
/**
 * Implementation of hook_field().
 */
function cck_table_field($op, &$node, $field, &$items, $teaser, $page) {
  switch ($op) {
    case 'validate':
      $allowed_values = content_allowed_values($field);
      if (is_array($items)) {
        foreach ($items as $delta => $item) {
          $error_element = isset($item['_error_element']) ? $item['_error_element'] : '';
          if (is_array($item) && isset($item['_error_element'])) unset($item['_error_element']);
          if ($item['value'] != '') {
            $lines = explode("\n", $item['value']);
            $lines = array_map('trim', $lines);
            $lines = array_filter($lines, 'strlen');

            $cell_count;
            foreach ($lines as $line) {
              if(!$cell_count) {
                $cell_count = count(explode('|', $line));
              } elseif($cell_count != count(explode('|', $line))) {
                form_set_error($error_element, t('%name: mis-align number of columns.', array('%name' => t($field['widget']['label']))));
                break;
              }
            }
          }
        }
      }
      return $items;
  }
}
?>