demo? :\but you were playing together. so i assume thats registered net game, even if used on lan. so i dunno.i would retry using a clean install each of blockland, and before installing addons.
You build with.. your... dad..?
1. Leave him alone2. Well, dont bump and dont do multiple posts3. Like my friend BisJac said, clean re-install Blockland4. Just to announce something: Some add-ons dont work for me but i never got Blockland braked from an add-on!