There has been several people reporting the missing sidebar issue before and this has to do with WP e-commerce and the way they have coded their templates. I have seen threads at their forum reporting the issue too, as well as various hacky workarounds with limited success.
Luckily, I just recently saw that someone had dug out the reason for the conflict and reported it at Thematic's googlecode as a bug, though there is nothing wrong with Thematic. He/she had contacted the WP e-commerce team but they were not inclined to fix it on their side.
The solution: remove a WP e-commerce function from a hook and reattach it with a lower priority so that it will fire after the sidebars has been set up. Add this in your child theme's functions.php file:
function switch_ecommerce_actions() {
remove_action('template_redirect', 'wpsc_all_products_on_page');
add_action('template_redirect', 'wpsc_all_products_on_page', 20);
}
add_action('init','switch_ecommerce_actions');
This is because "wpsc_all_products_on_page" does an "exit" at the end, thereby stopping any execution after it. By giving this function a lesser priority, we make sure Thematic can set up it's sidebars first.
If you are a member of their forum, maybe you could post the solution there as well? I think there are many people that would benefit from this.
