pcmanfm: 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/pcmanfm - from package: pcmanfm

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

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