Won't erase...

[NealF]

I'm in AST 11 and starting to use Frame by Frame. Still a bit of a newbie to ASP.

Here's what I'm trying to do:
1. Create the first frame in a FBF layer.
2. Duplicate the frame.
3. Erase the part of the picture that I want to animate, leaving the rest the same as the first frame so as not to have to redraw it all.

It all works fine until I use the eraser to try to erase some of the second frame. I get a checkerboard pattern where I erase but it doesn't erase anything. Also tried using the other end of my Wacom stylus. Nothing.

Don't know if it matters, but I've got two FBF layers. The bottom one is a pencil sketch and the top one is a few clean ink lines. I'm going to eventually have the bottom sketchy lines do the squiggly look (animate outlines) and keep the clean lines static for the look that I want. So I do need two layers of fbf.

Thanks.