Hi,
The way I see it, you have 3 main choices.
1. You can amend your conditional lookup formulas so that they do not return #N/A error values. This is going to create a pretty long formula so possibly not the best option.
2. You can keep your lookup formulas and then use a helper column. The helper column would contain formulas such as this:
Code:
=IF(ISNUMBER(B2),B2,)
where B2 contains the lookup formula. You would then sum this helper column.
3. You can create a sum formula which sums the lookup formula results and has the capacity to ignore error values. A formula which does this is:
Code:
=SUMIF(B2:B10,"<=9.99999999999999E307")
where B2:B10 contains your lookup formulas.
Hope that helps...