The title pretty much says it.
I have a custom taxonomy term "Topics", which is otherwise functioning smoothly. When I try to add individual taxonomy terms from that Taxonomy to a custom nav menu (yes, on a custom theme), they show up highlighted in red with the word "invalid" where the term name normally would be.
I am using the interface found at http://www.mysite.com/wp-admin/nav-menus.php.
I can still add categories, individual posts, tags, and categories. I can even add custom post type archive pages using the plugin "Add Custom Post Types Archive to Nav Menus".
If anybody has any information that can help me to understand why this is happening, I would be very appreciative. Thank you so much for your time!