xx-diff-proxy: 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/xx-diff-proxy - from package: xxdiff-scripts

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

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