zMask

I don’t get what is going wrong. I did a zMask and it worked great. I go back and try it again - and it doesn’t work. It seems like pure chance. Does anyone else find this or did I perhaps do something wrong?

I click on the layers I want to render. Ctrl Left on the layer to mask according to. Click on Zmask. Render: I get a black screen as my final render.

Nevermind - I figured it out. I had to make that layer visible in edit mode.