lancelot: 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 CentOS possible default full paths are:

/usr/bin/lancelot - from package: kdeplasma-addons

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/lancelot - from package: plasma-widget-lancelot

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

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