mpswap: 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/mpswap - from package: mpdtoys

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

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