xmousepos: 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/xmousepos - from package: xautomation

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

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