dropbearconvert: 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/dropbearconvert - from package: dropbear

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

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