lit2epub: command not found

Have You tried accessing the binary with the full path?

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/lit2epub - from package: epub-utils

You may install the required package with command apt-get install {package}
Error in other languages:
lit2epub: bevel nie gevind nie
lit2epub: comandă negăsită
lit2epub: comando não encontrado
lit2epub: commande introuvable
lit2epub: command not found
lit2epub: käsku ei ole
lit2epub: không tìm thấy lệnh
lit2epub: komanda nerasta
lit2epub: Kommando nicht gefunden.
lit2epub: kommandot finns inte
lit2epub: komut yok
lit2epub: nie znaleziono polecenia
lit2epub: níor aimsíodh an t-ordú
lit2epub: no se encontró la orden
lit2epub: no s'ha trobat l'ordre
lit2epub: opdracht niet gevonden
lit2epub: parancs nem található
lit2epub: perintah tidak ditemukan
lit2epub: príkaz nenájdený
lit2epub: příkaz nenalezen
lit2epub: команда не найдена
lit2epub: командата не е открита
lit2epub: 命令找不到
lit2epub: コマンドが見つかりません