Mail Merge Math - Syntax Error

Hello. I'm trying to perform the following calculation on merge fields in Word 2003:
{ =(({ MERGEFIELD "BuyerLotPrice" }-{ MERGEFIELD "BuyerLotIncentive" })+({ MERGEFIELD "BuyerBaseHousePrice" }-{ MERGEFIELD "BuyerBaseHouseIncentive" }))}

My goal is this in normal math terms:
(BuyerLotPrice-BuyerLotIncentive) + (BuyerBaseHousePrice-BuyerBaseHouseIncentive)

I keep getting "Syntax Error". The document recognizes the amounts of each field individually, it just isn't performing the math.

Assuming I typed everything correctly above since it wouldn't paste, can anyone tell me what I'm doing wrong? This is my first attempt at mail merge math, though I'm familiar with Excel math and somewhat familiar with database fields. I've tried different google searches to solve this on my own, and I just cannot find a good resource for syntax help for this subject. Thank you.