Like you, I thought of putting fake values back into the cube's Calculation script rather than using WITH. I wanted to figure out whether null came from:

1. No calculation being performed at all

2. The THEN part of the IIF statement

3. Something going wrong in the subtraction within the ELSE part of the IIF statement.

So I tried this:

CREATE MEMBER CURRENTCUBE.[Measures].[Net Lost Commitments (during period)]

-- AS null

AS 9990

, FORMAT_STRING = '#,#'

, ASSOCIATED_MEASURE_GROUP = 'Commitment Measures'

, DISPLAY_FOLDER = 'Time-based Commitment Measures'

, VISIBLE = true;

SCOPE (DESCENDANTS([Date Dimension].[Fiscal Year Hierarchy],,AFTER));

-- [Net Lost Commitments] can only be calculated if [Growth in Commitments] can be,

-- and that is only possible if just one member is selected from the date dim.

-- So if referring to [Date Dim].currentMember fails (probably coz multiple members have been selected) then return null.

[Measures].[Net Lost Commitments (during period)] =

iif(iserror([Date Dimension].[Fiscal Year Hierarchy].CurrentMember)

--, null

--, [Measures].[Acquisitions (during period)] - [Measures].[Growth in Commitments (during period)]);

, 9991

, 9992);

END SCOPE;

SCOPE (DESCENDANTS([Date Dimension].[Calendar Year Hierarchy],,AFTER));

[Measures].[Net Lost Commitments (during period)] =

iif(iserror([Date Dimension].[Calendar Year Hierarchy].CurrentMember)

--, null

--, [Measures].[Acquisitions (during period)] - [Measures].[Growth in Commitments (during period)]);

, 9993

, 9994);

END SCOPE;

... and then ran this query ...

select

{[Measures].[Net Lost Commitments (during period)]

,[Measures].[Net Lost Commitments (during previous period)]

} on columns

, {[Date Dimension].[Fiscal Year Hierarchy].[Fiscal Month].AllMembers} on rows

from Compass3

The results were [Net Lost Commitments (during period)] = 9992 for all periods (that's what I expect) -- *except* [Dec-2010] in which case the value shown is 9990.

Comment 1: Every time I rebuild, the null values seem to move around. In this case, the anomaly does not show up at the Year level but at the Month level.

Comment 2: I have just checked (again!) the order of measure definitions. Every measure in the calculation script is defined later in the script than any measure on which it depends.

Comment 3: The value 9990 implies that no calculation is being performed: that value is specified *outside* the SCOPE statements. So why would this one member of the date dimension not be covered by the SCOPE?