Tutorial Quick preview generate error?

macroScript QuickPreview category:"HowTo"

(
preview_name = (getDir #preview)+"\quickpreview.avi"

view_size = getViewSize()

anim_bmp = bitmap view_size.x view_size.y filename:preview_name

for t = animationrange.start to animationrange.end do

(
slidertime = t

dib = gw.getViewportDib()

copy dib anim_bmp

save anim_bmp

)

close anim_bmp

gc()

ramplayer preview_name ""

)