Hi,
HikaShop can display several payment methods, that's not a problem. You can see that on our demo website's checkout for example.
I've never seen a case where the payment methods selector would display the error message after you select another payment method.
When you get that error, most of the time, it comes from a setting of the payment method not configured properly.
Here is a FAQ which lists the different things you can check:
www.hikashop.com/support/documentation/106-faq.html#paym
Please check each point listed there.