Created a different field to group by and its working now.
Do you understand why the first SQL did not work?
Use of functions in the GROUP BY clause is restricted.
This might have worked...
"SELECT Sum(Line_Item_Total), MONTH(actual_setup_Date) as MON, YEAR(actual_Setup_Date) as YR FROM CUSTOMER GROUP BY MON, YR"; ""; "")
PS bad form to answer your own question
Unfortunately that style also don't work on FM.
The column named "MON" does not exist in any table in the column reference's scope.
GROUP BY allows only column(field) name.