Ah.... I probably wouldn't worry about the message in the console then. Turns out it's from the @{spellcasting_ability} Attribute. On NPCs with no spellcasting ability, this is set to 0*, and PC is complaining about this not being a valid Attribute call. You can change it to reference an ability if you want to get rid of that console message, you can point it towards a random Attribute. @{caster_level} would do the trick, should always be 0 on anything with the spellcasting_ability set to 0*. I can't find the error message anywhere in the PC or PCM code. Maybe it's coming from R20? I'm not sure, someone else probably knows more about it.