Hopefully someone already knows this. I have a suitelet that i have created a form with a checkbox field. I am updating that field with the defaultValue from a customer record. The customer record has a checkbox with the

true

value but the suitelet is complaining with the error

You have entered an Invalid Field Value true

You already figured this one out but I'll add my experience to the collective knowledge. In my experience when you add body fields to the form or column fields to a Sublist (e.g. in a Suitelet or beforeLoad user event), Field.defaultValue and Sublist.setSublistValue() only accept strings. So checkbox fields require 'T' or 'F', and date fields require a string instead of a date object.