Hi,
You can try selecting parts of the formula in the formula bar, and pressing
F9, which evaluates the selection.
You have to select a piece of the formula that can stand on its own. eg, you
could select:
VLOOKUP(TYPE,ProductData,6,FALSE)
or
Spacg8
or
BBGROUT+BEAM*EA*QTY
or
HALF*Setup!$C$15,HALF*Setup!$C$17
or
IF(ISBLANK(LINTEL),HALF*Setup!$C$15,HALF*Setup!$C$ 17))
or
Setup!$C$19*CORNERS/2)

Each of these should return a value or a True/False. If any of them returns
the Value error, then the problem is contained within that selection.

Hope this helps
Regards - Dave.