gvncviewer: 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/gvncviewer - from package: gvncviewer

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

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