diffpos: 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/diffpos - from package: survex

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

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