upbibtex: 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/upbibtex - from package: texlive-binaries

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

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