BackupPC_sendEmail: 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/share/BackupPC/bin/BackupPC_sendEmail - from package: BackupPC

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

On Debian possible default full paths are:

/usr/share/BackupPC/bin/BackupPC_sendEmail - from package: BackupPC

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

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