There's dimension DimTable1 containing in Column1 a lot of duplicate values, NULL values and '' values. Processing the Cube fails with an error:
Errors in the OLAP storage engine: A duplicate attribute key has been found when processing: Table: 'dwh_DimTable1', Column: 'Column1', Value: ''.
However it used to work properly with all this data before. And after I'd updated the '' values to 'default' it also processed successfully. The question is what's wrong with this data, why it allows duplicates, nulls but not empty strings? The Cube definition hasn't been changed recently.
Null vales get converted to empty string.
as a test I'd try updating your column to be non empty string data and process data.