pwi2xsf: 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/pwi2xsf - from package: xcrysden

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

Error in other languages:
pwi2xsf: bevel nie gevind nie
pwi2xsf: comandă negăsită
pwi2xsf: comando não encontrado
pwi2xsf: commande introuvable
pwi2xsf: command not found
pwi2xsf: käsku ei ole
pwi2xsf: không tìm thấy lệnh
pwi2xsf: komanda nerasta
pwi2xsf: Kommando nicht gefunden.
pwi2xsf: kommandot finns inte
pwi2xsf: komut yok
pwi2xsf: nie znaleziono polecenia
pwi2xsf: níor aimsíodh an t-ordú
pwi2xsf: no se encontró la orden
pwi2xsf: no s'ha trobat l'ordre
pwi2xsf: opdracht niet gevonden
pwi2xsf: parancs nem található
pwi2xsf: perintah tidak ditemukan
pwi2xsf: príkaz nenájdený
pwi2xsf: příkaz nenalezen
pwi2xsf: команда не найдена
pwi2xsf: командата не е открита
pwi2xsf: 命令找不到
pwi2xsf: コマンドが見つかりません