On which of the above is your layout based?
If Tenant or Park, is there a related record in SystemVariable? "Allow creation" does not mean "automatically create". Some database action to create the related record must take place before the related record is created.
The layout is based on Tenant.
I got it to work by playing around, but I'm not so sure I understand why.
I would guess that you didn't have a related record in the System variable table.