checkflac: 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/checkflac - from package: flactag

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

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