annotate module error

Im new in module development. I tried to use annotate module example from Pro Drupal development book and I have strange error.

I can’t save Annotations per node and other settings. I can’t reset it to default. And I alwaye getting “Please enter a number.” Even if I have set number.

I made output echo “out = ”.$form_values['annotation_limit_per_node'];
But it’s empty

Glad if anybody could point out if I have configured anything wrongly.

Drupal 5.2

/** 
 * Define the settings form. 
 */ 
function annotate_admin_settings() { 
  $form['annotate_nodetypes'] = array( 
    '#type' => 'checkboxes', 
    '#title' => t('Users may annotate these node types'), 
    '#options' => node_get_types('names'), 
    '#default_value' => variable_get('annotate_nodetypes', array('story')), 
    '#description' => t('A text field will be available on these node types to make user-specific notes.'), 
  );
  
  $form['annotate_deletion'] = array( 
    '#type' => 'radios', 
    '#title' => t('Annotations will be deleted'), 
    '#description' => t('Select a method for deleting annotations.'), 
    '#options' => array( 
      t('Never'), 
      t('Randomly'), 
      t('After 30 days') 
    ), 
    '#default_value' => variable_get('annotate_deletion', 0) // default to Never 
  );
  
  $form['annotate_limit_per_node'] = array( 
    '#type' => 'textfield', 
    '#title' => t('Annotations per node'), 
    '#description' => t('Enter the maximum number of annotations allowed per node (0 for no limit).'), 
    '#default_value' => variable_get('annotate_limit_per_node', 1), 
    '#size' => 3 
  );
  
  // Define a validation function. 
  $form['#validate'] = array( 
    'annotate_admin_settings_validate' => array() 
  );
    
  return system_settings_form($form); 
}

// Validate the settings form. 
function annotate_admin_settings_validate($form_id, $form_values) { 
  if (!is_numeric($form_values['annotation_limit_per_node'])) { 
    form_set_error('annotate_limit_per_node', t('Please enter a number.')); 
  } 
}