We are using cube writebacks to update cell values. Sometimes the cell
are empties, the cube writeback works great in that case too, storing
it's delta from zero.

Here is the dilemna: how to "update" a specific cell to be empty again?
(it was empty, no fact, then a first UPDATE CUBE filled it -- now we
want to revert to the previous stage, the person wants to remove it's
data). If I just put the value to zero, it's not empty, it's zero, and
then it's counted for averages when it shouldn't.

We only have an XML/A connection to the olap source, and would rather
not touch the fact table directly / reprocess the cube. Any way to set
a cell value to empty using MDX?

Thanks in advance,

Brice.