MDX syntax to get ID of a hierarchical value

Hi,

I'm trying to create a dimension to obtain the ID of the Current Member of a hierarchical structure Date.

E.g.: I need the ID of the selected value in the filter March-2013.

The syntax I've tried is:

[Fecha].[Fecha].CurrentMember

When I run the query I select March-2013 in he filter, but the query is showing the ID ALL istead of the current member.

Any ideas? Thanks in advance!

Florencia