gtg_new_task: 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/gtg_new_task - from package: gtg

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

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