purgeCentralCache: 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
/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/share/lemonldap-ng/bin/purgeCentralCache - from package: liblemonldap-ng-portal-perl

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