cssconvert: 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/cssconvert - from package: dspam-hash

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

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