I can't get there from here

Original post

It would appear to me that everything to the left of the red line works.

Element.SetParameterByName is wanting an element as the input. You are feeding in a value. What element do you want to change?

All the elements that have negative values shown in the watch box directly to the left of the red line.

In the lists directly to the left of the red line, you just seem to have the (filtered) calculated values from the Schedule. There’s no way to find the original elements from those values.

One way forward would be to collect (say) ID numbers from the schedule at the same time as you get the calculated values. Then you could filter those lists of IDs and use them to retrieve the relevant elements from Revit.