xmlsec1-config: 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/xmlsec1-config - from package: xmlsec1-devel

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

On Debian possible default full paths are:

/usr/bin/xmlsec1-config - from package: libxmlsec1-dev

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

Error in other languages:
xmlsec1-config: bevel nie gevind nie
xmlsec1-config: comandă negăsită
xmlsec1-config: comando não encontrado
xmlsec1-config: commande introuvable
xmlsec1-config: command not found
xmlsec1-config: käsku ei ole
xmlsec1-config: không tìm thấy lệnh
xmlsec1-config: komanda nerasta
xmlsec1-config: Kommando nicht gefunden.
xmlsec1-config: kommandot finns inte
xmlsec1-config: komut yok
xmlsec1-config: nie znaleziono polecenia
xmlsec1-config: níor aimsíodh an t-ordú
xmlsec1-config: no se encontró la orden
xmlsec1-config: no s'ha trobat l'ordre
xmlsec1-config: opdracht niet gevonden
xmlsec1-config: parancs nem található
xmlsec1-config: perintah tidak ditemukan
xmlsec1-config: príkaz nenájdený
xmlsec1-config: příkaz nenalezen
xmlsec1-config: команда не найдена
xmlsec1-config: командата не е открита
xmlsec1-config: 命令找不到
xmlsec1-config: コマンドが見つかりません