You need to add a count field to dataset using query below

COUNT(1) OVER (PARTITION BY ProductName) AS Cnt

and then use it in expression for background color as

IIF(val(Fields!Cnt.Value) > 1 ,"Blue","White")

If you can change dataset you need to add a parent grouping on the report based on ProductName field and use expression as below

IIF(Count(Fields!SomeField.Value,"GroupName") > 1 ,"Blue","White")

I have a weekly report with multiple products due for manufacture on the same day. viz. - 

02/09/15 Product A
02/09/15 Product B
03/09/15 Product A
04/09/15 Product C
04/09/15 Product X

I need to highlight any product that appears more than once in the report. e.g. Product A

What is the best way to achieve this ?

Hi Superdata,

The BackgroundColor property for the detail row

=Switch(Count(Fields!ProductName.Value, "WeekGroup") = 1, "Red"
    , Count(Fields!ProductName.Value, "WeekGroup") > 2, "Green")

Hi Milan

This doesn't work as every row is now highlighted Green.  I just want to highlight the duplicates e.g. product A