alvesjc,
I'm not sure what you're doing, but it looks like the functions you're calling expect pointers to PinDescriptions objects, and that you're giving them actual PinDescription objects rather than pointers. So the -> operator (which may be implicit in that function even though you can't see it) fails. See here for an explanation:
So I can't tell from your code which variables are PinDescriptions, but if you put an ampersand in front of them, you'll be converting them to pointers and then the -> operator will work.
So if RS is a PinDescription, try digitalPinToPort(&RS).