PKCS10Client: 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/PKCS10Client - from package: pki-java-tools

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

Error in other languages:
PKCS10Client: bevel nie gevind nie
PKCS10Client: comandă negăsită
PKCS10Client: comando não encontrado
PKCS10Client: commande introuvable
PKCS10Client: command not found
PKCS10Client: käsku ei ole
PKCS10Client: không tìm thấy lệnh
PKCS10Client: komanda nerasta
PKCS10Client: Kommando nicht gefunden.
PKCS10Client: kommandot finns inte
PKCS10Client: komut yok
PKCS10Client: nie znaleziono polecenia
PKCS10Client: níor aimsíodh an t-ordú
PKCS10Client: no se encontró la orden
PKCS10Client: no s'ha trobat l'ordre
PKCS10Client: opdracht niet gevonden
PKCS10Client: parancs nem található
PKCS10Client: perintah tidak ditemukan
PKCS10Client: príkaz nenájdený
PKCS10Client: příkaz nenalezen
PKCS10Client: команда не найдена
PKCS10Client: командата не е открита
PKCS10Client: 命令找不到
PKCS10Client: コマンドが見つかりません