ctndisp: command not found

Have You tried accessing the binary with the full path?

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/ctndisp - from package: ctn

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