Check your Sources/Subs.php file to ensure the shop section was added properly. Find:
// Make sure the administrator has a valid session...
Add below (if it doesn't already exist):
//Begin SMFShop code
loadLanguage('Shop');
if (allowedTo('shop_admin'))
$context['admin_areas']['shop'] = array (
'title' => $txt['shop_admin'],
'areas' => array(
'shop_general' => "<a href='$scripturl?action=shop_general'>{$txt['shop_admin_general']}</a>",
'shop_inventory' => "<a href='$scripturl?action=shop_inventory'>{$txt['shop_admin_inventory']}</a>",
'shop_items' => $txt['shop_admin_items'],
'shop_items_edit' => "|--- <a href='$scripturl?action=shop_items_edit'>{$txt['shop_admin_items_addedit']}</a>",
'shop_restock' => "|--- <a href='$scripturl?action=shop_restock'>{$txt['shop_admin_restock']}</a>",
'shop_usergroup' => "<a href='$scripturl?action=shop_usergroup'>{$txt['shop_admin_usergroup']}</a>",
)
);
//End SMFShop code