headerthemeeditor: 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/headerthemeeditor - from package: kmail

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

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