If a user puts the 'embed' code into the multimedia URL instead of the shared URL, they are presented with HTTP Status 404 error. When this happens, the 'edit' link is not clickable and the only way to remove the item is to remove the Lessons tool and recreate.
The problem was code to show the resources path. Unfortunately if you put < into a URL, the path in resources will have < in it. The code for outputting the path was not quoting it properly. For a real test, you need to do add resources and add multimedia, and possibly other types, with a reasonable file name or URL and various unreasonable ones. Make sure that it doesn't disable editing on the page, and that in the edit dialog the path shows as reasonable. I think I've got it right, but who knows?
If a user puts the 'embed' code into the multimedia URL instead of the shared URL, they are presented with HTTP Status 404 error. When this happens, the 'edit' link is not clickable and the only way to remove the item is to remove the Lessons tool and recreate.
Example URL:
<iframe width="420" height="315" src="http://www.youtube.com/embed/-Kou0HBpX4A" frameborder="0" allowfullscreen></iframe>