mwc-ace: 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/mwc-ace - from package: mpc-ace

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

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