Looks like the module is expecting this structure:
modules/jquery_ui/jquery.ui/(actual jquery ui files)
However, it looks like jQuery UI library removed the version.txt file that this module checks for. If it does not find that text file, it considers the plugin 'not installed' which is kind of a bad check.
People are talking about it here, with a fix for Drupal 6 (and some talk for 7): https://www.drupal.org/node/1954136
However the project page advises you to use jQuery Update instead:
Drupal 7+ Since Drupal 7 ships with jQuery UI, the jQuery UI module
has been deprecated and moved to the jQuery Update module.
You should dump this module and use jQuery Update and go from there.