bibtex.pybtex: 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/bibtex.pybtex - from package: pybtex

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

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