cairo-dock-session: 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/bin/cairo-dock-session - from package: cairo-dock-core

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

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