ltsp-build-client: 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/sbin/ltsp-build-client - from package: ltsp-server

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

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