You have attempted to apply a numerical expression, which is not uniquely defined for the specific variable. In order to use this variable in expressions relying on number of occurrences, please read it a second time under a new name from its primary table.
What does it mean to "... read it a second time under a new name from its primary table."?
I am getting this message when creating a Chart Field Expression to sum order totals using dimension of 'state' in from an orders table.