Well, altenbach had covered 2 of the 3 errors I covered.
The third error is that you have a case "Calculation of PV" that is undefined in your enum. You need to define that case in your enum constant.
The rest of the explanation is a way to prevent the error from popping up again when you to add yet another case. And to prevent having to update each of the rapidly growing number of enum constants that will populate your diagram.
Since you are new to LabVIEW, I would recommend looking at the online LabVIEW tutorials
LabVIEW Introduction Course - Three Hours
LabVIEW Introduction Course - Six Hours
