Would need sample data to help further; including all the data tables involved. Are you copy and pasting from your app the exact code?
Also noticed upon looking again, do you really want a Sum of distinct volumes in pie?
Is there a volume and BF_Volume?
Why does _vBFLastYear have a num() and _vCurrentYear not?
Set analysis is very finicky, be sure every piece/variable evaluates as expected by placing values in a text object. Poorly formed Set Analysis may syntactically check but yield an empty set or have no effect if the expression evaluates to null