putprop error

I have the following callback function called everytime something
changes in a toggle field.
I am getting the following error


*Error* putprop: first arg must be either symbol, list, defstruct or
user type - nil

Here is my callback procedure


procedure( toggleCB(form field)
  let((fieldValue toggleValue lastValue)
    ;; get the current value of the field
    fieldValue = getq(get(form field) value)
    ;; obtain the toggle value, which is the last value in the list
    toggleValue = car(last(getq(get(form field) value)))
    ;; store a custom property on this field to mark the last value
    lastValue = putpropq(get(form field) !toggleValue storedValue)
    printf("I'm breaking in ToggleAll\n")
    ;; when the current toggle value is not the same as the stored
value
    ;; set the values all on if the toggle is on, or all off otherwise
    when(toggleValue != lastValue
      if(toggleValue
        putpropq(get(form field) mapcar(lambda((x) x t) fieldValue)
value)
        putpropq(get(form field) mapcar(lambda((x) x nil) fieldValue)
value)
      ); if
    ); when
  ); let
)

It is erroring out in the putprop statements.

Could you tell me what is that Iam doing is wrong