mpdcheck: 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 CentOS possible default full paths are:

/usr/bin/mpdcheck - from package: mpich2

You may install the required package with command yum install {package}

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