Sometimes error messages in word bear no relation to the error.
You can see what fields there are using the Opt+F9 keyboard shortcut. (On some computers Fn+Opt+F9)
This toggles display of field codes.
For IF fields, the maximum number of nested levels is 20, but you are nuts if you are using that many.
Here is my article on dealing with fields in Word:
https://answers.microsoft.com/en-us/msoffice/forum/all/dealing-with-fields-in-microsoft-word/e1bdddad-5a51-4327-837c-c3786c16a501