Define the default member for non-aggregatable attributes in either the DefaultMember property or the cubes' MDX script
This rule analyzes dimensions that contain non-aggregatable attributes to determine whether a default member is defined.
Best Practices Recommendations
You should define the default member for non-aggregatable attributes. Otherwise, Analysis Services will select an arbitrary default member for each attribute.
Unlike aggregatable attributes, non-aggregatable attributes do not have an (All) member to use as the default member. Because non-aggregatable attributes have no obvious default member, the server selects an arbitrary member to be the default member for each attribute. The server uses this arbitrary default member whenever the non-aggregatable attribute is not explicitly included in a Multidimensional Expressions (MDX) query.
To avoid having an arbitrary member selected as the default member, explicitly set a default value for each non-aggregatable attribute. You can explicitly set the default member on the DimensionAttribute object or in the MDX script of the cube.
For More Information
For more information, see Configuring the (All) Level for Attribute Hierarchies in SQL Server Books Online.