Date / Year variances between years

Hi, I am quite new to Olap,and have been using excel 2007 as the olap browser. I have come to a problem that I cannot solve - In fact I have been at it for the past 2 days, and frankly close to giving up.
The problem is that I have a collumn named customer, and have a drilldown for product, and across I have 2 years for analysis.

Customer code Value 2007 Value2008
Products Value 2007 Value2008

What I am after is the Value2008 less Value2007. I have tried the following formula but am getting an error The '2007' string cannot be converted to the date type.


The output for the above is a variance, however I can live with a formula to get 2007 values, and 2008 values in a separate formula and then subtract.
Thanks in anticipation for anyone who can help.

-- USING FORMULA

SUM
(([Date].[monthly analysis].[year].&[2007]),[Measures].Value
)

Did you try to use the function you show, are you proposing to use it, or are you asking how we would suggest doing it?

We'll try to help with more particulars ...

Bill