isql-vt: 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 CentOS possible default full paths are:

/usr/bin/isql-vt - from package: virtuoso-opensource-utils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/isql-vt - from package: virtuoso-opensource-6.1-bin

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

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