USERELATIONSHIP function can only use the two columns references participating in relationship.

in this tutorial, Create-reports/desktop-dimensional-model-report ,on creating new measure 

1. Sales Amount by Due Date = CALCULATE(SUM(Sales[Sales Amount]), USERELATIONSHIP(Sales[DueDateKey],'Date'[DateKey]))

2. get the error    USERELATIONSHIP function can only use the two columns references participating in relationship.
3. highly appreciate solution to