you cannot conditionally sum like you had
you can either make a new formula field to sum (at any group level) like
If year({OrderLineItem_sql.DateBilled})=Year(Currentdate)-1 then {OrderLineItem_sql.qty_shipped} else 0
or you can make a running total with an evaluate formula to conditionally count
name= whatever
field to summarize= OrderLineItem_sql.qty_shipped
type of summary = sum
evaluate=use a formula
year({OrderLineItem_sql.DateBilled})=Year(Currentdate)-1
reset=at group 1 if you want values for each group
palce in group footer (RTs do not work in headers)