Purchase - registration process does not work.

-- url of the page with the problem -- : slcst.com
-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.5.28
-- PHP version -- : 5.5.0
-- Browser(s) name and version -- : Chrome any
-- Error-message(debug-mod must be tuned on) -- : unused
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, This email address is being protected from spambots. You need JavaScript enabled to view it. and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.

oomla installed.
I register a client and this email is sent for verification:

Hi John Adams,
Thank you for registering at slcst.com/ .
Your account must be activated by clicking on the link below. You will then be able to continue your order.

slcst.com/index.php?option=com_hikashop&...&task=activate&activ ation=c970c3cdd34226fa9abcf397893057d1&infos=eyJwYXNzd2QiOiJwYXR0b24xMjMiLCJ1c2V ybmFtZSI6ImphZGFtcyJ9&page=checkout&id=11&lang=

You can log in the website with the following username and password.
Username : jadams
Password : patton123

I click on the link and the server sends this:

unused
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, This email address is being protected from spambots. You need JavaScript enabled to view it. and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.

I am trying to locate the error in the logs or at least see if there is an error in the logs.

Where or how can I access them? Or is it something you guys have to access for me?
Thank you.

As a new user I was able to navigate through to the purchase of a shirt to the point where the total amount for the sale is shown. I changed the 5 quantity to 1 and got this error:
slcst.com/index.php/component/hikashop/product/listing
Fatal error: Call to a member function getParents() on null in /home/snakeshaker/slcst/components/com_hikashop/views/product/view.html.php on line 880
I'll go test again.

I can now get to the Paypal page. So, this may work.
So, the solution for me was to disable the "extra" security configured on the Dreamhost control panel.