Level 1 exam - model building activity 2

Typically when receiving this message it means that the modules being used are built on a hierarchical list and there is no natural aggregation to display - this can occur when you are leveraging data from a summary point to drive a calculation at a lower level in the hierarchy (i.e. disaggregation). 

In this instance I would recommend double checking the "Applies To" in the source module (DAT02) - are those lists the same as being leveraged in REV02?  If not, do the lists being used in REV02 have a parent hierarchy relationship to source lists?  If not, then either the module setup is incorrect or a system module is needed to map the list properties in order to leverage the SUM function.   *Hint: you should not need a SUM function here as SKU data will summarize to Products/Product Family.