I've did some addition to this plugin. Original plugin lets you add files and links, but provides no way to remove them from a lesson plan. My updates adds "Del" after each link or file and when clicked it deletes the data from the lesson plan. The old way of removing the files was to create a new lesson plan. So this is a helpful feature.
Anyone interested in the updated lesson.php file can email me at email@example.com
I wish I could take over development of the plugin as the Authors appear to have abandoned it. Their site is gone and no updates since 2007.