Hi,
I have just installed two versions of a site with the ModusVersus template on the same Xampp environment.
One is your demo site and one is a Joomla 3.5.1 site with the ModusVersus template installed.
The Joomla 3.5.1 generates a series of warnings/notices that the Joomla 3.1 version used by the demo website does not.
As they both run on the same Xampp environment, I assume that these are Joomla 3.5.1 compatibility issues.
I have seen a previous answer on this forum that these are 'only' warning messages, but they do not occur with the Joomla 3.1 installation and to be honest, I am a bit worried by even warning messages, especially as they also show up in the backend, the configuration page of the template.

On the frontpage the errors in the menu area are:
Warning: Invalid argument supplied for foreach() in C:\xampp-joomla\basis\htdocs\templates\numodusversus\includes\helper.php on line 283
Notice: Undefined index: Open Sans in C:\xampp-joomla\basis\htdocs\templates\numodusversus\includes\helper.php on line 298
Notice: Undefined index: query in C:\xampp-joomla\basis\htdocs\templates\numodusversus\includes\helper.php on line 300
Notice: Undefined index: family in C:\xampp-joomla\basis\htdocs\templates\numodusversus\includes\helper.php on line 301
and in the main content area (joomla article):
Notice: Undefined property: stdClass::$tags in C:\xampp-joomla\basis\htdocs\templates\numodusversus\html\com_content\featured\default_item.php on line 120
Notice: Trying to get property of non-object in C:\xampp-joomla\basis\htdocs\templates\numodusversus\html\com_content\featured\default_item.php on line 120

On the template configuration page the errors are:
Warning: SimpleXMLElement::attributes(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 866
Warning: property_exists(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 869
Warning: property_exists(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 869

I am aware of the fact that this is a free template, but... it is a template that is very much to my liking, and I would have happily paid for it if it had been a commercial template.

O, yes. The 3.5.1 site has K2, Simple Image Galery Pro and Frontpage Slideshow installed. All of them the latest versions.

So my real question is: are these errors 3.5.1 related or do I need to finetune the parameters or settings? If it si 3.5.1 related, I don not need to bother trying to fix them. If not, I need to fix them.

Hello,

On the template configuration page the errors are:
Warning: SimpleXMLElement::attributes(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 866
Warning: property_exists(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 869
Warning: property_exists(): Node no longer exists in C:\xampp-joomla\basis\htdocs\libraries\joomla\form\field.php on line 869

These are notices from Joomla! itself. They are coming from core files which cannot be altered.

The rest of the issue are simply notices, they will not affect the site's functionality in any way.
You can deactivate them by going to your site's global configuration and deactivate error reporting.

Krikor,
thank you for your answer.
I slighhtly misinterpreted the meaning of error messages. I overlooked the fact that there are multiple sources for error messages, so I disabled error messages at PHP.ini level, something I prefer not to do in a test environment.
Now that you point out that the messages are generated by Joomla itself, this means I can switch PHP errror messaging back on and disable the joomla level messages.

There is no reason to edit the php.ini file, since Joomla! offers this functionality by default.

Yes, notices and strict standards can be generated by Joomla! as well as other extensions. Deactivating error reporting will make sure that these are not shown and furthermore they are not printed in any JSON or RSS feeds.

PS. Nice dog :)

The dog is Ziggy, my Sharpei, when he was 6 months old. He is 5 years old now.
Amazing dog as he loses his wrinkles when he gots older while I only get more wrinkles...

Such a charming gent :)