ykparse: 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/ykparse - from package: libyubikey

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

On Debian possible default full paths are:

/usr/bin/ykparse - from package: libyubikey-dev

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

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