I'm using forge version 1.12.2-forge-14.23.5.2855 and SBM-CardboardBoxes-1.12.2-0.0.2b12.jar (I believe that's the latest stable version for 1.12.2) in the configs I've set:

blacklistsettings {
    # Prevents mobs spawners from being placed into cardboard boxes [default: true]
    B:BlackListMobSpawners=false
}

and in tile_ban_list I've set:

# Clazz[TileEntityMobSpawner] [default: true]
B:"minecraft:mob_spawner"=false

any help?

@GHXX or @bl4ckscor3 can I get you to check into this... as day job has me spent.

From my testing this fix should have no effect on other cardboard boxes (pre-existing as well as new ones). This is just used to determine the block to place/name to display in addInformation as far as I can tell.

Tested the fix some more, and found no further issues. Will release a new version now.