mousepad: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/mousepad - from package: mousepad

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