purple-send-async: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/purple-send-async - from package: libpurple

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

On Debian possible default full paths are:

/usr/bin/purple-send-async - from package: libpurple-bin

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