Ch. 16 Compiling a SWF from a CSS

[fantasticphil]

Hello all and hope im in the right spot, saw in another post that this
forum is for 3 and 4. I am working in the flex 4 training from the
source book.

In chapter sixteen the book states that I can select "Compile CSS to
SWF" everything worked out fine till I got to Chapter 17 and the
section "Customize Button States with skins". I got to the end of the
exercise and noticed that my "defaultStore" was throwing two errors
that stem from not recognizing the FlexGrocerButtonSkin.mxml. Took me
a little while to realize that I still had "Compile CSS to SWF" still
checked. Although I can move on with unchecking I am still curious as
to why it wasnt recognizing my Button Skin. Do you know why it was
throwing these errors?

Thanks for the help.