I'm unable to delete a plugin. There is no "Uninstall" link in the Plugin Overview page. If I delete the directory, Moodle tells me that the plugin is "Missing from disk".
What are possible causes for this? It's an authentication plugin that I've created myself. Could there be something wrong with my code?
I was wondering whether it cannot be removed because there are users who have registered using it. However the "Uninstall" link didn't appear despite deleting all the users created with it.
I'm using Moodle 2.7+ (Build: 20140515).