When trying to set a date value using the Macro system you need to make sure that you have the correct date format.
The following SQL will return a date format that can be used to set a field:
SELECT TO_VARCHAR(T0."DocDueDate", 'yyyy-mm-dd') FROM "ORDR" T0 WHERE T0."DocNum" = 972
The format needs to be 'yyyy-mm-dd' for it to work.