There are some changes made to scripting, they are listed in the Change Log.
For object properties, you no longer use brackets "()" so for example zone.bestDescription() becomes zone.bestDescription and zone.number() becomes zone.number. Brackets are now only used for methods, like message.show() or helper.alert()
That's likely the cause of the error.
This is a one time change, it will make scripting more readable and straightforward.
If you are still getting the error after making this change, please paste the entire function code.