Please note the Once Off Costs calculated for an Idea are driven by the specified list of Investment types, 

Once-off costs = Investments(Capex or Opex) - Benefits. As a result, if the benefits are more than the investments the value, it will mean you will have a negative once-off cost. i.e. 

The Once Off Costs for this Idea will be calculated as.

         Once off costs = Investments(Capex or Opex) - Benefits = 150 0000 - 0 = 150 000