Case statement issue in MDX query....?

With 
MEMBER [Measures].[Week4] AS
	( [Measures].[Teu], [Date].[Week].CurrentMember.Lag(3) )
MEMBER [Measures].[Week3] AS 
	( [Measures].[Teu], [Date].[Week].CurrentMember.Lag(2) )
MEMBER [Measures].[Week2] AS 
	( [Measures].[Teu], [Date].[Week].CurrentMember.Lag(1) ) 
MEMBER [Measures].[Week1] AS 
	( [Measures].[Teu], [Date].[Week].CurrentMember )

MEMBER [Measures].[WeekSum] AS        
     Sum({[Date].[Week].CurrentMember.Lag(3) : [Date].[Week].CurrentMember},
         [Measures].[Teu])
	
	Select {[Measures].[Week4],[Measures].[Week3],
	       [Measures].[Week2],[Measures].[Week1],
	       [Measures].[WeekSum]} on 0,
	   case when   [Dimtop].[Id].&[1]=[Dimtop].[Id].currentmember then   
	       Topcount([Commodity _flat].[Commodity].[Commodity].Members,5,[Measures].[WeekSum])
	   when    [Dimtop].[Id].&[2]=[Dimtop].[Id].currentmember then 
	       Topcount([Commodity _flat].[Commodity].[Commodity].Members,10,[Measures].[WeekSum])
	     else  
	       Topcount([Commodity _flat].[Commodity].[Commodity].Members,25,[Measures].[WeekSum])  
	       End on 1

	       From [Commodities]
	       where (Strtomember("[Date].[Week].&[2012010101]",CONSTRAINED),
	           Strtomember("[Dimtop].[Id].&[2]",CONSTRAINED))

HI.,

         here case statement fails for second condition., kindly suggest  where the mistake is..?

The output is always first condition. returns only top 5..,

Thanks, Avula.GK