Cannot delete Add Note to Delete Text coments (Acrobat XI)

Most of the time, when I right click, the delete option is missing.  Sometimes, when I check properties, the locked box is checked and when I uncheck it, the delete option reappears. Most of the time, though, the locked box is unchecked. Anyone know how to fix this issue globally? Is there some preference that I have selected that defaults to locking the deletion of comments?  Thanks.