When editing a command block's last output via /blockdata or /give (with NBT), if there is a space in the specified LastOutput tag, "An unknown error occurs".
When editing a command block's last output via /blockdata or /give (with NBT), if there is a space in the specified LastOutput tag, "An unknown error occurs".
Why in the world are you changing the LastOutput ? That's more or less just a read-only field updated by the command block.
Anyway, please provide the commands you're using.