xx-cvs-diff: 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-cvs-diff - from package: xxdiff-scripts

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

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