send_nsca: 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/sbin/send_nsca - from package: nsca-client

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

On Debian possible default full paths are:

/usr/sbin/send_nsca - from package: nsca-client
/usr/sbin/send_nsca - from package: nsca-ng-client

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

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