hncgen: command not found

Have You tried accessing the binary with the full path?

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/hncgen - from package: hdf

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