sff-load: 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/sff-load - from package: sra-toolkit

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

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