rv_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/rv_merge - from package: why

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

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