Xtightvnc: 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/Xtightvnc - from package: tightvncserver

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

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