Here it is... I turned on from layer drop down menu "freeze or thaw in current viewport" Layer "A-_ANOTVPRT_P-" and viewports reappeared... You may also consider that that layer is not plottable - use command "layer" and you'll see that that option is marked red - unplottable...
M.R.
Hope this helps...
Firstly I thought this was the problem, but I was wrong... Anyway, someone could do this so consider it also :
(defun c:vpsvisibility ( / adoc pspcoll psplst ch)
(vl-load-com)
(setq adoc (vla-get-activedocument (vlax-get-acad-object)))
(setq pspcoll (vla-get-paperspace adoc))
(vlax-for ent pspcoll
(setq psplst (cons (vl-catch-all-apply 'vla-get-objectname (list ent)) psplst))
)
(setq psplst (reverse psplst))
(princ psplst)
(prompt "\nPress ENTER to continue")
(textscr)
(command pause)
(initget 1 "Yes No")
(setq ch (getkword "\nDo you want to turn on/off visibility <Yes/No> : "))
(vlax-for ent pspcoll
(if (= ch "Yes")
(vla-put-visible ent :vlax-true)
(vla-put-visible ent :vlax-false)
)
)
(princ)
)