tpbconv: 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/tpbconv - from package: gromacs

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

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