convert_pgn: 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/convert_pgn - from package: convert-pgn

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

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