pngchunkdesc: 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/pngchunkdesc - from package: pngtools

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

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