xhtml2ps: 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 CentOS possible default full paths are:

/usr/bin/xhtml2ps - from package: xhtml2ps

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/xhtml2ps - from package: xhtml2ps

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

Error in other languages:
xhtml2ps: bevel nie gevind nie
xhtml2ps: comandă negăsită
xhtml2ps: comando não encontrado
xhtml2ps: commande introuvable
xhtml2ps: command not found
xhtml2ps: käsku ei ole
xhtml2ps: không tìm thấy lệnh
xhtml2ps: komanda nerasta
xhtml2ps: Kommando nicht gefunden.
xhtml2ps: kommandot finns inte
xhtml2ps: komut yok
xhtml2ps: nie znaleziono polecenia
xhtml2ps: níor aimsíodh an t-ordú
xhtml2ps: no se encontró la orden
xhtml2ps: no s'ha trobat l'ordre
xhtml2ps: opdracht niet gevonden
xhtml2ps: parancs nem található
xhtml2ps: perintah tidak ditemukan
xhtml2ps: príkaz nenájdený
xhtml2ps: příkaz nenalezen
xhtml2ps: команда не найдена
xhtml2ps: командата не е открита
xhtml2ps: 命令找不到
xhtml2ps: コマンドが見つかりません