velveth_63_long: 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/velveth_63_long - from package: velvet-long

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

Error in other languages:
velveth_63_long: bevel nie gevind nie
velveth_63_long: comandă negăsită
velveth_63_long: comando não encontrado
velveth_63_long: commande introuvable
velveth_63_long: command not found
velveth_63_long: käsku ei ole
velveth_63_long: không tìm thấy lệnh
velveth_63_long: komanda nerasta
velveth_63_long: Kommando nicht gefunden.
velveth_63_long: kommandot finns inte
velveth_63_long: komut yok
velveth_63_long: nie znaleziono polecenia
velveth_63_long: níor aimsíodh an t-ordú
velveth_63_long: no se encontró la orden
velveth_63_long: no s'ha trobat l'ordre
velveth_63_long: opdracht niet gevonden
velveth_63_long: parancs nem található
velveth_63_long: perintah tidak ditemukan
velveth_63_long: príkaz nenájdený
velveth_63_long: příkaz nenalezen
velveth_63_long: команда не найдена
velveth_63_long: командата не е открита
velveth_63_long: 命令找不到
velveth_63_long: コマンドが見つかりません