xnecview: 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/xnecview - from package: xnecview

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

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