EventFinder module does not find css file in multi-site configuration

I have installed a directory EventFinder containing EventFinder.module and EventFinder.css in a subdirectory modules of my Drupal 'sites' directory, to support a multi-site configuration.

Although EventFinder module registers and appears to work otherwise, it reports an error in Watchdog:

Type	page not found
Date	Saturday, December 10, 2005 - 23:27
User	admin
Location	/pressroom/modules/eventfinder/eventfinder.css
Referrer	http://og.civicspacelabs.org/pressroom/admin/settings/eventfinder
Message	modules/eventfinder/eventfinder.css not found.
Severity	warning