Can't add brushes to preset library

I'm trying to add sets of brushes to my preset library but it won't work. The files load into the preset manager box, but I can't save them. The "Save set" button is not activated (just "Done" "Append" and "Add".) I can use the brushes I add or append during that session, but as soon as I close or restart they are gone. Help? I'm running Photoshop Elements 2018 on Windows 10.