gtab-merge: 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/gtab-merge - from package: gcin

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

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