lxsession-default-terminal: 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/lxsession-default-terminal - from package: lxsession

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

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