I am trying Bezier masking for the first time, Vegas Pro 421. I'm trying to follow this tutorial.

When the effect is dragged onto the timeline at 1.08 in the video, a rectangle appears on the preview window in the video, this does not appear for me. When he plans to draw a curve at 5.40 mouse icon changes to a pen tip, this happens on my screen. When I click in the window like he does at 5.45, unlike the video no corner point appears.

I suspect somehow my preview window is frozen as when I press play, either under the timeline or under the window, the line on the timeline (sorry can't recall it's name) moves but nothing happens in the preview window. I suspect I have something set incorrectly, probably something simple, but just can't figure out what. Any help is appreciated