FvwmCommand: 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/FvwmCommand - from package: fvwm

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

On Debian possible default full paths are:

/usr/bin/FvwmCommand - from package: fvwm

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

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