This ain't a Client Error, its a swf or Furnidata.xml error, which i dont know what to do
1. Check if item_ids in catalog_items match to id in furniture.
2. Check if sprite_id in furniture matches to id in furnidata.
3. Make sure you are using the updated SWF, and not for pre-update.
4. Say :update_items, :update_catalogue, clear cache, and reload.
It should work after this.