mutt_dotlock: 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/mutt_dotlock - from package: mutt

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

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