Server Error 500 on Orders in joomla administrator

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.6
-- PHP version -- : 5.4.45-2
-- Browser(s) name and version -- : Chrome/Firefox
-- Error-message(debug-mod must be tuned on) -- : Server Error 500 when I click on Orders in backend administrator of joomla site with Hikashop
It's url is this

/administrator/index.php?option=com_hikashop&ctrl=order&order_type=sale&filter_partner=0

In backend of joomla 3.4.6 / Hikashop 2.6.0 if you click on Orders I get a Server Error 500.

Hi,

Please check your PHP error log or set temporally the "error reporting level" to "maximum" in your Joomla global configuration.
The "error 500" is not the real error message ; we need that information in order to be able to understand the issue and provide a fix.

Regards,

Thanks for your response.

Here is the error message with error reporting set to maximum

Notice: Undefined index: s0ed5e in /var/www/vhosts/mackaymaternitywear.com.au/httpdocs/plugins/system/highlight/highlight.php on line 1

Fatal error: Cannot redeclare o06a6314e() (previously declared in /var/www/vhosts/mackaymaternitywear.com.au/httpdocs/layouts/joomla/toolbar/link.php:1) in /var/www/vhosts/mackaymaternitywear.com.au/httpdocs/layouts/joomla/toolbar/link.php on line 1

Ok it's been hacked. We'll take site down and clean it out.

Hi,

Regarding the error message ; I'm afraid that you have been hacked.
As you can see in the incriminated files, HikaShop is not related to your issue, but the recent security issue in Joomla could be related.
Please re-install Joomla in your website in order to use the official files and be sure that nothing has been modified.
For more details ; please use the Joomla support forum.

Regards,