How to use MDX Functions in SAP dreamweaver's MDXTEST

This is more or less the query I'm after:

WITH [Measures].[rowcount] AS
  COUNT([SomeDimension].Members)

SELECT
  [Measures].[rowcount] ON ROWS

FROM
  [FOO/BAR]

Ultimately I'm after a row count of the fields after some 20 dimensions are applied - for data profiling purposes. But I can't get even this little snip to execute. The editor just dumps me directly into the ABAP debugger (where I have absolutely no expertise).

Any advise on what's going wrong? Thanks!

Here is a working example tested on SAP BW IDES EHP7.

WITH MEMBER [Measures].[rowcount] AS  COUNT([0D_NW_CODE].[LEVEL01].MEMBERS * [0D_NW_PLANT].[LEVEL01].MEMBERS )
SELECT {[Measures].[rowcount] } ON COLUMNS FROM [$0D_NW_C01]