myproxy-logon: 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/myproxy-logon - from package: myproxy

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

On Debian possible default full paths are:

/usr/bin/myproxy-logon - from package: myproxy

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

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