possible problems
you messed with the textures (reinstall the map)
someone you know messed with the textures (reinstall the map)
blockland is messed up (reinstall)
before you reinstall blockland go to a different map with sand.
if i recall there is some sand a bit out in bedroom look there see if it's pink.
if so then reinstall blockland or find someone on the forums to
give you that sand texture.
i would but i don't have blockland installed or have a key right now so I'm not going to install blockland.