mtp-sendtr: 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/mtp-sendtr - from package: libmtp-examples

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

On Debian possible default full paths are:

/usr/bin/mtp-sendtr - from package: mtp-tools

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

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