sff-load.2: 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.2 - from package: sra-toolkit

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

Error in other languages:
sff-load.2: bevel nie gevind nie
sff-load.2: comandă negăsită
sff-load.2: comando não encontrado
sff-load.2: commande introuvable
sff-load.2: command not found
sff-load.2: käsku ei ole
sff-load.2: không tìm thấy lệnh
sff-load.2: komanda nerasta
sff-load.2: Kommando nicht gefunden.
sff-load.2: kommandot finns inte
sff-load.2: komut yok
sff-load.2: nie znaleziono polecenia
sff-load.2: níor aimsíodh an t-ordú
sff-load.2: no se encontró la orden
sff-load.2: no s'ha trobat l'ordre
sff-load.2: opdracht niet gevonden
sff-load.2: parancs nem található
sff-load.2: perintah tidak ditemukan
sff-load.2: príkaz nenájdený
sff-load.2: příkaz nenalezen
sff-load.2: команда не найдена
sff-load.2: командата не е открита
sff-load.2: 命令找不到
sff-load.2: コマンドが見つかりません