the product x is not available, but is option

-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.4.8
-- Browser(s) name and version -- : safari
-- Error-message(debug-mod must be tuned on) -- : The product Beschikbare data: 9 - 16 juli is not available
The product Aantal deelnemers: 1 persoon is not available

I've created some products with options ("aantal deelnemers" en "beschikbare data"). Now I want to test/walk through the whole process.
But as soon as I get to the checkout page, it tells me the following:

The product Beschikbare data: 9 - 16 juli is not available
The product Aantal deelnemers: 1 persoon is not available

But those are the options for the product.....
Why does it tell me this? And what can I do to fix it?

But when I turn that on it looks like this, see attachment.

And that is weird, because these options are for choosing for how many persons you want to book the course and for what week...
I thought that was what te options were about.... To choose "properties" for the product.... I don't want these separate on the cart.

How should I solve that?

It should be like choosing a color or size....

Oh I see that when I set "Group options with product" to YES, it looks ok. OK that fixes it