I have created my first cube, and am confused by the Grand Total column results. I have sales amount, quantity, and commissions paid measures in my cube.  I have confirmed that all numbers are correct until the quantity numbers roll up into the Grand Total column in the cube browser, these results are incorrect.   For example, I have three years of sales quantity data that when totalled down are correct:  2006 = 1,054,949; 2007 = 770,7737; 2008 = 428,543, yet the Grand Total of these three years =  -2,040,735.  I have gone through the Aggregations wizard, however I have obviously done something wrong. My sales & commission dollar amounts are correct in individual years as well as the Grand Total.  My quantity is an integer data type with a sum aggregation, and I am using SQL '08.  Any ideas where I can find what is causing this Grand Total error?

Thanks in advance for the help!

Correct, I am viewing it in the browser in BIDS (but I get the same result when I look at the data in Excel); I do not have an calculation created in MDX. 

I thought if I drilled down to the lowest level I would find incorrect data, but there are no negative numbers in the data – yet to total is a negative number. 

You sometimes see this with large numbers adding up to overflow an integer value; they turn into negative numbers. Granted, your numbers here shouldn't cause that, since Int32 can go to ~2.1 billion and you seem to be around 2.1 million. Still, change the data type of the measure to BigInt and reprocess to see what happens.