nmapsi4: 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/nmapsi4 - from package: nmapsi4

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

Error in other languages:
nmapsi4: bevel nie gevind nie
nmapsi4: comandă negăsită
nmapsi4: comando não encontrado
nmapsi4: commande introuvable
nmapsi4: command not found
nmapsi4: käsku ei ole
nmapsi4: không tìm thấy lệnh
nmapsi4: komanda nerasta
nmapsi4: Kommando nicht gefunden.
nmapsi4: kommandot finns inte
nmapsi4: komut yok
nmapsi4: nie znaleziono polecenia
nmapsi4: níor aimsíodh an t-ordú
nmapsi4: no se encontró la orden
nmapsi4: no s'ha trobat l'ordre
nmapsi4: opdracht niet gevonden
nmapsi4: parancs nem található
nmapsi4: perintah tidak ditemukan
nmapsi4: príkaz nenájdený
nmapsi4: příkaz nenalezen
nmapsi4: команда не найдена
nmapsi4: командата не е открита
nmapsi4: 命令找不到
nmapsi4: コマンドが見つかりません