All of the fields must be filled.
You cannot swap a section with a page.
You must first select a group before adding a user to it.

Alright, so if you've ended up here, you probably saw a billion links on google mentioning how to configure tinymce but they all end up mentioning drupal or some other implementation and you just want a quick and functional answer. Well, my friend, you've come to the right place! Let's take a look at how we can very quickly and easily configure multiple instances of tinymce or have some textareas remain plain and others use tinymce.