Hello David,
thank you very much! It worked like a charm.
I also added this php snippet from Tom to make sure that the sidebars for this specific category are enabled:
add_filter( 'generate_sidebar_layout','generate_custom_category_sidebar_layout' );
function generate_custom_category_sidebar_layout( $layout )
{
// If we are on a category, set the sidebar
if ( is_category( 'Blog' ) )
return 'both-sidebars';
// Or else, set the regular layout
return $layout;
}