Error when using Aster

I was going through one of the tutorials and ran in to an error the prevents me from going any further with the tutorial. This is the tutorial and I am at the point at which I am supposed to Select a main shape from the object browser, but instead of being able to move on with the next button in the wizard, I get an error message stating "The selected object in not a main shape". I get other errors when selecting some of the other items in the object browser, but I imagine that is due to most of them not being geometry.

How to I fix this? I get the same error message with any other piece of geometry I try to select. I tried the help button, but the help is in French.