ppmtolss16: 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 CentOS possible default full paths are:

/usr/bin/ppmtolss16 - from package: syslinux-perl

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ppmtolss16 - from package: syslinux-utils

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

Error in other languages:
ppmtolss16: bevel nie gevind nie
ppmtolss16: comandă negăsită
ppmtolss16: comando não encontrado
ppmtolss16: commande introuvable
ppmtolss16: command not found
ppmtolss16: käsku ei ole
ppmtolss16: không tìm thấy lệnh
ppmtolss16: komanda nerasta
ppmtolss16: Kommando nicht gefunden.
ppmtolss16: kommandot finns inte
ppmtolss16: komut yok
ppmtolss16: nie znaleziono polecenia
ppmtolss16: níor aimsíodh an t-ordú
ppmtolss16: no se encontró la orden
ppmtolss16: no s'ha trobat l'ordre
ppmtolss16: opdracht niet gevonden
ppmtolss16: parancs nem található
ppmtolss16: perintah tidak ditemukan
ppmtolss16: príkaz nenájdený
ppmtolss16: příkaz nenalezen
ppmtolss16: команда не найдена
ppmtolss16: командата не е открита
ppmtolss16: 命令找不到
ppmtolss16: コマンドが見つかりません