dpatch-convert-diffgz: 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

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/dpatch-convert-diffgz - from package: dpatch

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