PSnonmem and GGPLOT

It's hard to see, but let's try. Here is vpcfig2 with everything between the opening and closing parentheses symbolized:

vpcfig2(vpcdir = "A", vpctab = "B",
vpcresult = "C",use.model.path = TRUE ... {similar arguments}, fy = function(y) { y }, fx = function(x) { x }, xlab = ("Time, hrs "), ... {similar arguments})

or even more symbolically, vpcfig2(x) which is syntactically a function, but it hasn't been defined as such; there's not anything in the form, except within the parens

vcpfig2 <- function(x) {x = 2x}

To go further, it would be helpful to know what kind of graph you're looking to produce and a FAQ: What's a reproducible example (`reprex`) and how do I do one?, which would be a representative chunk of your variables or fabricated values in the same form.

If you have an image of the output you're looking for, that would be very helpful as well.