Hi,
Can you activate the "debug mode" and "error reporting" settings of the Joomla configuration and try again ?
That should display an error message with more information on the issue so please provide it.
If not, then please look in the php error log of your server for the fatal error message corresponding to that issue so that we can better understand the situation.
Also, the version number you've provided doesn't exist.
So either you're using HikaShop 2.6.2 (and not the 3.6.2) and you might want to update HikaShop to the latest version to fix that issue; or you're using already the latest version of HikaShop, but you want to turn off the "checkout legacy" setting of the HikaShop configuration in order to use the new checkout system of HikaShop, which can hopefully help fix that issue.