Hi guys,
As free store modules go I find the Web Warehouse one made by
Emerald Solutions is quite easy to use.
It has one bug I know of in the sense that once you've created a category you can't delete it (I've reported this to them with no response!) but you can hide categories you don't want to display by archiving so it doesn't the shop's function.
One tip though is to follow their advice on their FAQ pages for installing.
Also ensure the shop front page is always the same (dont point the page in Admin>Pages to a different URL like a specific category page else you'll get
this error [since the Store Admin module knows the location of the shop front page through the shop's page name as it appears in the navigation menu])
Hope that's useful,
GuChuSum.