apngasm: 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/apngasm - from package: apngasm

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

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