Warning on clear cache about plugin openlayers_simple

When I clear cache, with drush or from UI, on my logs I see this:

Plugin openlayers_simple of plugin type boxes:plugins points to nonexistent file sites/all/modules/contrib/openlayers/includes/boxes/openlayers_simple.inc for class handler handler.

In Openlayers that file is under "plugin" directory, not under includes.
Why does it search it there?
I've also tried to copy the file there, but it doesn't change.

How can I solve?

Thanks,
Sergio