Hi @compell
Sounds like an update has happened from a much older version of ACF which used to use a function called ‘register_options_page’.
Can you please use the function here:
http://www.advancedcustomfields.com/resources/functions/acf_add_options_sub_page/
If this is not defined, then perhaps the issue is that your add-on is not loading by the time you run the code. Are you including the add-on in a theme? Or is it a normal plugin?
Thanks
E
