SYMPTOM:
When browsing elements for a certain attribute under Data Explorer, the following error appears in Strategy Developer:

SQLEngine got an Exception from DFC: Engine Logic: HDA-MDX error due to one of the following reasons: (1) A hierarchy on the template must be related to one or more attributes in the report filter, or it cannot be replaced by one (or multiple) attributes. (2) A global attribute is missing the default lookup table or local attribute is missing its source table. (3) Local Attributes from more than one MDX SourceTable is not supported yet!

ACTION:
Edit the attribute and set "Browse Sort" to None for all the MDX attribute forms. A Schema Update is required so the changes take effect.