Help with Vla-Put-ModelView

This is my first attempt to manipulate AcDbViewport Objects (learning exercise), and cannot seem to find the solution on my own.

I've successfully created an viewport in PaperSpace at the correct location, and already have a named Model view, but for some reason cannot successfully apply said view to the viewport.

Snip:

;; Create viewport
(setq vp
 (vla-addpviewport
   (vla-get-paperspace *activeDoc*)
   (vlax-3d-point '(8.6477 5.56637 0.0))
   16.0
   9.84))

;; Set view
(vla-put-modelview vp (vla-item (vla-get-views *activeDoc*) "1"))

The latter portion returns this error:

; error: Automation Error. Description was not provided.
_$ 

... Which is confusing as there is no description called for from the developer documentation; only the Object (PViewport), and the ModelView (View object).

Any help would be greatly appreciated!