A workaround has been found, thanks to an earlier post from Karim (Karim_Bernardet1) about the very same error. I believe it has something to do with the type of single quote being keyed in.
A link to that thread for reference - [ODK2] Calculation - #5 by Satish_Ravishankar
It would be useful to understand how to type in the correct single quote using the keyboard.
In the interest of figuring out a solution rather than workaround, I will leave this topic as unsolved.