plessc: 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/plessc - from package: php-lessphp

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

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