tightvncconnect: 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/tightvncconnect - from package: tightvncserver

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

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