If I understand your question I would recommend a different approach.
What I think you want is to filter by group (invoice) where any record in the group is equal to a specific product.
For a crystal only solution you can create a formula to flag the records you want to keep.
As an example:
formula 'flag' as
if field = 'specific product' then 1
group on invoice number
Now summarize 'flag' as a SUM at the invoice group level
Now any group that had the value you are looking for has a value >0 and all the others = 0.
Go into the select expert and change it to use 'group select' and add your criteria here
SUM(flag,invoice)>0
Edited by DBlank - 03 Feb 2011 at 4:39am