parallel-scp: 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

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/parallel-scp - from package: pssh

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