In some of the older instances, tabbed forms is not an option for a user to select. They must go create a user preference for tabbed forms.
Instead of creating single-user preferences for tabbed forms the user has an option to create a system-wide user preference for tabbed forms.
Go to user preference and create a new preference with the following info:
type: true| false
Tabbed forms do not work in UI15. PRB682544. KB0622649