One way you can check to see what is causing the issue is to build the calculation piece by piece. In other words, start with the following-- IF [ACCOUNTING WEEK #] >= 4 THEN [SALES UNITS] END -- and then, if that works, add in the next part IF [ACCOUNTING WEEK #] >= 4 AND [YEAR] >= 2012 THEN [SALES UNITS] END .
If you still see issues, I would be happy to take a look at it if you could provide a sample dataset. Also, what is your underlying datasource if you don't mind me asking?
Hope this helps,