drupal doesn't find plugin on multisite

Hi

i would to reuse this module like i did, but for sometimes drupal doesn't find the plugin.So i try to reinstall, and drush tell me :

Module jquery_ui doesn't meet the requirements to be enabled.                                           [error]
The jQuery UI plugin is missing. Download and extract it into the sites/all/libraries directory. Rename [error]
the extracted folder to jquery.ui. (Currently using jQuery UI Not found)

i don't understand why jquery ui stop working for a while...
any idea ?

thanks