Named sets and Existing

I have a very large Account dimension (> 2,000,000 members). I would like to create a named set for the top most profitable accounts. I plan to use this named set in the SSRS Report Builder to compensate for its lack of aTop N feature. The problem is that the user can change the fiscal period and SSAS needs to reevaluate the set. Using Generate function won't work for performance reasons. So, I'm trying to use Existing to force the set generation. e.g.

CREATE SET CURRENTCUBE.[Top 5 Profitable Accounts]

AS

Order(TopCount(

(EXISTING [Account].[Account].[Account].Members, [Period].[Period].CurrentMember), 5, [Measures].[Profit]),

[Measures].[Profit], DESC);

However, this gives me "The Period hierarchy already appears in the Axis1 axis." error when I test the set with the following query

select non empty [Measures].[Profit] on 0,

non empty [Top 5 Profitable Accounts] on 1

from [RPM]

WHERE [Period].[Period].&[20030228]

and duplicated dimensionality error in the Report Builder.

Does anyone know how this could be implemented?

There are a couple of issues in the Named Set:

The error can be eliminated by not explicitly specifying [Period].[Period].CurrentMember with Existing.|||

Deepak,

Thank you for helping. True, the modified set doesn't error out. However, as you pointed out, it is not dynamic. It only works with the default time period which is where I started. In other words, EXISTING doesn't help here. Changing the query slicer to a different time period doesn't produce any results. It looks like we cannot change the context of standard named sets defined with CREATE SET in the cube script. This pretty much leaves me with no options to simulate TopN with the Report Builder.