probemodem: 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/sbin/probemodem - from package: hylafax+

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

On Debian possible default full paths are:

/usr/sbin/probemodem - from package: hylafax-server

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

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