gnatprep: 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/gnatprep - from package: gcc-gnat

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

On Debian possible default full paths are:

/usr/bin/gnatprep - from package: gnat-4.9

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

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