fn-Not error in button appearance or ribbon appearance

I have run into an error when trying to use fn-Not when setting the visibility or ribbon settings on a button.

When i use this formula:

I get a hard SharePoint error when opening the form.

This, on the other hand, works as expected, just in reverse of what i need it to do:

Can anyone see anything wrong with the equation or can reproduce.

I am using Forms 1023 Version: 2.11.8.30

Thanks, in advance.

Ed