regconvert: 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/regconvert - from package: regina-normal

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

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