error 500 on server header checker

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.5

Hi,
i receive some advises from bing and Google and some of my pages are disappearing from indexing. So i'm investigating and i discoverd that on the pages of Hikashop i have the response of 500.
I explain better.
On the front end of my site i see the categories and the products fine but if i test them with:
www.stepforth.com/resources/server-heade...r-tool/#.VjoXzLcvfb1
and with
tools.seobook.com/server-header-checker/

-http://www.lacasettabio.it/negozio-online/olio-extravergine-d-oliva
for the category i have
HTTP/1.1 500 Class view non trovata [class, file] => categoryViewproduct, /home/lacasett/public_html/components/com_hikashop/views/product/view.html.php

-http://www.lacasettabio.it/negozio-online/olio-extravergine-d-oliva/prodotto/libro-il-meraviglioso-mondo-olivo-olio-extravergine-oliva-vendita-online
for the product i have
HTTP/1.1 500 Layout default non trovato

I think it is this the origin of my indexing problem.
Could you help me please?
Thanks a lot
My best regards

Hi,
thanks for your help.
I disabled every site cache and the jch optimizer plug-in.
Then I disabled one by one every system plug-in.
Then i tryed to disable all the system plug-in together.
I'm sorry, the issue is still present.
The issue is not present with the article of joomla but it is present only with hikashop.
Could you give some more help, please?
My best regards

Hi,
thanks again for your help.
I've tryed to disable the hikashop plug-in
Then I've tryed to disable the modules
Then i've tryed to change the template to the joomla template Protostar
Then I've tryed to come back to the default joomla htaccess
I'm sorry, never is change
i have Always that strange error 500.
So, what could you recommend now?
Maybe is it better if i open a ticket on my server provider?

Hi,
here i am again!
My server provider've checked and tested my site and, they said , that from your hand it is ok.
They've checked the server logs several time and there are no errors on a server side.
After that there was a migration to a more performer server with a new platform that runs entirely on Solid State Drives (SSD).
The error is not gone!
So they discovered that it seems that this error is presented only on a few online testers, like the tools.seobook.com/server-header-checker one.
They have tested the page with other tool and the results was Status: HTTP/1.1 200 OK

Now, what can i do?
I have Bing that report me a lot of error 500 and i suspect that, maybe, the origin was the same.

Do you tested some other Hikashop sites with the same online tester? What is the response?
Best regards

Hi,
i suppose that you ment "bug" insted "but".
If yes, so, you think we can stay just like we stay, without worry, isn't it?
best regards