Possibly, just some sort of access issue somewhere. You were substituting in the profile view of a field. So for example if the field isn't set to display on profile such a substitution won't output anything. Same for if the tab is set to a view access level the user can't access, etc.. Couple different access checks that could cause that, but if you don't need formatting (most fields don't have special HTML, etc..) then [FIELD_NAME] will be fine.