Error getting the Highiest/Lowest value

[mersimbakalli95]

Hi everyone, 

I am new with JasperSoft. I want to create two variables, showing Highiest/Lowest value of a column Total from some invoice records. I have placed the variables into summary part, evaluation time Report but when I preview i get this error for both: net.sf.jasperreports.engine.JRException: net.sf.jasperreports.engine.fill.JRExpressionEvalException: Error evaluating expression for source text: <<variable name here>>

Also I want to use those variables to create conditional formatting for this Total column.  So when a total value equals highiest it shows in blue, lowest in red.

Any help?

Thank you