Take care when move module

• put the add-on modules at drupal/sites/all/modules/
  instead of drupal/modules/ , where core modules are put.
  
  
• if an add-on module was placed at drupal/modules/,
  before moving it to drupal/sites/all/modules/, remember to disable it first.
  Then cut and paste the whole diretory of the add-on module to drupal/sites/all/modules/