pto_merge: command not found

Have You tried accessing the binary with the full path?

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/pto_merge - from package: hugin-tools

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