I put the end of the if/then/else formula into it's own formula and it works fine: tonumber({CI_Item.ShipWeight})*{SO_PickingSheetWrk.QuantityOrdered} So it's tied to another piece of the if/then/else state statement - I think it's the if isnull({CI_Item.ShipWeight}) then 0 - which doesn't cause a problem when the else result is: tonumber({CI_Item.ShipWeight})*{SO_PickingSheetWrk.QuantityOrdered} so strange, it just doesn't make sense. Anyway, is there a simple formula to say if the result of tonumber({CI_Item.ShipWeight}) is not a number or causes an error then 0? If I can throw that in there in case there are any bad/non-numeric ship weights I think I'll be good.