Can't install modules from UI when site placed in subdirectory
You have to uncomment this line. 

  # Modify the RewriteBase if you are using Drupal in a subdirectory or in a
  # VirtualDocumentRoot and the rewrite rules are not working properly.
  # For example if your site is at http://example.com/drupal uncomment and
  # modify the following line:
  # RewriteBase /drupal


Another option is to update module using drush.

drush up