Conditional Palette in Bar Chart ( op-err-0131 )

[w0nger]

I've created a bar chart and tried to add a conditional palette based on an expression comparing two data items.

If Data1 < Data2 then make the bar red.

Data1 is the primary axis and Data2 is a colored region.

I've tried adding Data2 to the Property-Properties for the Primary Axis Member Node, however, I still get the OP-ERR-0131 Measure valueSet="Data1" can not have another measure as an attribute: groupBody="Data2"

Is there a solution?