Sorry if I was stating the obvious if I had a Pound for everytime I've been scratching my head over a software/hardware problem only for the answer to be staring me in the face I'd be much better off than I am now.
The first time you use it, Candy Bar should automatically back up your default icons on my system (running Tiger) they're stored in ~/Library/Application Support/Candy Bar. Clicking on the 'Restore Icons' button should, well, restore the icons, even after your trial licence has expired. However, I think that if you've already customised your system icons before Candy Bar has run for the first time it'll copy the changed icons not the original Apple system icons. Are you by any chance running any other GUI software a theming app such as Shapeshifter for example?