HttpClient: 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/HttpClient - from package: pki-java-tools
/usr/lib/ruby/gems/1.8/gems/httpclient-2.4.0/bin/httpclient - from package: rubygem-httpclient

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

On Debian possible default full paths are:

/usr/bin/HttpClient - from package: ruby-httpclient

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

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