Why Mondrian do that with this query?

[martosoler]

I'm doing this query....
WITH MEMBER [Measures].[Supermarket]
AS 'Filter([Store].[Store Name].Members, [Store].CurrentMember.Properties("Store Sqft") = 23593)'
select
{[Measures].[Store Sales]}
ON COLUMNS,
{[Measures].[Supermarket]}
ON ROWS
from [Sales]
And not work !!! The error is this:
Mondrian Error:No function matches signature 'Filter(<Set>, <Logical Expression>)'
But if I remove the 'WITH MEMBER' part and put in the rows axis like this:
select
{[Measures].[Store Sales]}
ON COLUMNS,
Filter([Store].[Store Name].Members, [Store].CurrentMember.Properties("Store Sqft") = 23593)
ON ROWS
from [Sales]
The query work, I'm doing something wrong or there is some concept that I don't know.
Thanks

[jhyde]

The Filter function returns a set of members. Yet WITH MEMBER requires a scalar expression. Use WITH SET instead.