isdncause: 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/bin/isdncause - from package: isdnutils-base

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

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