Analysis Services does not provide a way to sort dimension members in DESCending order, only in ASCending order.
Fortunately, this sort functionality is easy to implement, using the Data Source View.
Replace your table binding with a named query and create a new calculated column that you will use to order your dimension members.
Here is an example of such query:
SELECT DateKey, (-1)*CONVERT(int, Date, 112) as Days, Date FROM T_DATE
Where 'DATE' is your datetime column and 'DATEKEY' is your primary key.
Then, in the dimension definition, select the dimension key and set the following properties:
OrderBy: AttributeKey
OrderByAttribute: Days
And voilà, your dimension members are now ordered by the new attribute you created!
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