Registering a user using the normal joomla login

Registering a user using the normal joomla login form results in an error
Fatal error: Call to undefined function hikashop_decode() in /home/......./plugins/system/hikashopaffiliate/hikashopaffiliate.php on line 247
Joomla version is 2.5.11
Hikashop is business 2.1.2

Download manually HikaShop 2.1.3 on our website and install it on yours and that should fix the problem.