I've read such great things about Cassie's tutorials that I finally broke down and bought a couple tonight (one was on sale and the other I splurged and bought full price

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So I've been going through Custom Sticker and Clever Layering. Everything so far so good, except for one problem. I'm at the point of "clever layering" and when I follow the steps on pages 22-23 and release the Cmd key and put the cursor over the area I get a circle with a line through it and not an option for a cursor. When I try to select something I get a message that says "Could not use the eraser because more than one layer is selected." What am I doing wrong? Isn't that the point, for multiple layers to be selected?