myproxy-test: 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/myproxy-test - from package: myproxy-admin

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

On Debian possible default full paths are:

/usr/sbin/myproxy-test - from package: myproxy-admin

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

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