ubiblock: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/ubiblock - from package: mtd-utils

You may install the required package with command apt-get install {package}

Error in other languages:
ubiblock: bevel nie gevind nie
ubiblock: comandă negăsită
ubiblock: comando não encontrado
ubiblock: commande introuvable
ubiblock: command not found
ubiblock: käsku ei ole
ubiblock: không tìm thấy lệnh
ubiblock: komanda nerasta
ubiblock: Kommando nicht gefunden.
ubiblock: kommandot finns inte
ubiblock: komut yok
ubiblock: nie znaleziono polecenia
ubiblock: níor aimsíodh an t-ordú
ubiblock: no se encontró la orden
ubiblock: no s'ha trobat l'ordre
ubiblock: opdracht niet gevonden
ubiblock: parancs nem található
ubiblock: perintah tidak ditemukan
ubiblock: príkaz nenájdený
ubiblock: příkaz nenalezen
ubiblock: команда не найдена
ubiblock: командата не е открита
ubiblock: 命令找不到
ubiblock: コマンドが見つかりません