graphviz: 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:

/var/lib/wims/public_html/bin/graphviz - from package: wims

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

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