dispwin: 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/dispwin - from package: argyll

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

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