txt2tab: 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/lib/unicon/bin/txt2tab - from package: unicon-imc2

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

Error in other languages:
txt2tab: bevel nie gevind nie
txt2tab: comandă negăsită
txt2tab: comando não encontrado
txt2tab: commande introuvable
txt2tab: command not found
txt2tab: käsku ei ole
txt2tab: không tìm thấy lệnh
txt2tab: komanda nerasta
txt2tab: Kommando nicht gefunden.
txt2tab: kommandot finns inte
txt2tab: komut yok
txt2tab: nie znaleziono polecenia
txt2tab: níor aimsíodh an t-ordú
txt2tab: no se encontró la orden
txt2tab: no s'ha trobat l'ordre
txt2tab: opdracht niet gevonden
txt2tab: parancs nem található
txt2tab: perintah tidak ditemukan
txt2tab: príkaz nenájdený
txt2tab: příkaz nenalezen
txt2tab: команда не найдена
txt2tab: командата не е открита
txt2tab: 命令找不到
txt2tab: コマンドが見つかりません