SQL Query Left Outer join in SQL 2016

Hi Team,

Below query executing successfully on SQL 2008R2 but getting syntax error at Left outer join in SQL 2016, Kidly review and help me in rewriting the query. I tried to modify but error msg as--Invalid object 'aim_item'. And aim_item is not object in DB, it is derived sub query,. please help me

select item.item, item.itdesc, item.byid, item.listprice, item.oh, item.Oo, ITEM.AvgOh, Item.UserFcst, Item.FcstDemand, aimvendors.VAddress2, aimvendors.VCity, aimvendors.VName, aimvendors.VContact, aimvendors.VAddress1, aimvendors.Assort, item.itstat,

aimvendors.Vnid, aimusers.username,

sum(aim_item.period_ordered) period_ordered,

sum(aim_item.period_shipped) period_shipped,

sum((period_shipped*item.listprice)/1000) period_dol_shipped,

sum(aim_item.season_ordered) season_ordered,

sum(aim_item.season_shipped)...