Why does my nested formula work for some cells in the column but not all?

JakeK

#INVALID OPERATION is the error message I receive for some but not all cells.

=IF(AND([Created By Date]@row < TODAY(-365), [Target Completion Date]@row < TODAY()), "Red", IF(AND([Target Completion Date]@row >= TODAY(), ISBLANK([Project Status]@row)), "Yellow", IF([Project Status]@row = "Complete", "Green", IF([Target Completion Date]@row = 0, "Gray"))))

Rich Coles

Can you share examples of which cells it's not working for? Formula looks pretty robust to me, other than I would use "" instead of 0 in the last part ahead of "Gray", ie IF([Target Completion Date]@row = 0, "Gray")))) but that doesn't stop it working

Rich @ Prodactive