Date range ...

Hi,
I have to count the number of invoices between two dates (starting date and ending date).
I have a time dimension, and a another with the two dates.
I've created a measure :

Code Snippet

CREATE MEMBER [CTNAV].[Measures].[Nb]
AS count(
Filter
(
[Bon Vouchers].[N° Bon Vouchers].[N° Bon Vouchers].Members,
[Bon Vouchers].[Starting Date ].CurrentMember.MemberValue >=
[Time].[Date].CurrentMember.MemberValue
)
)

The problem is that if I display all the dates, each measure is at 0 but the total is ok (>0).

Sorry for my english.

Thanks for your help.