Hi,
Can you post your complete formula in the thread.
If you are using below logic,
IsNull({tblSOPartsUsed.Quantity})
or
({tblPriceBook.LaborHrsReq} * {tblSOPartsUsed.Quantity})
IsNull will give only Boolean value(True or False)
and
({tblPriceBook.LaborHrsReq} * {tblSOPartsUsed.Quantity}), will give values
the Output of the formula is different in both cases, thats why you are getting Boolean Required error.
Change your formula like below
if IsNull({tblSOPartsUsed.Quantity})
then 0
else
({tblPriceBook.LaborHrsReq} * {tblSOPartsUsed.Quantity})
--Praveen G