Hello,
You need to download the latest version of the SagePay plugin which has been updated some time ago in order to migrate from "mcrypt" to "openssl".
www.hikashop.com/marketplace/product/114-SagePay.html
For more details, don't hesitate to use the "contact us" form.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.