gri_merge: 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/gri_merge - from package: gri

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

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