Hi,
I suggest you to do like we did in our demo website for the computer product:
demo.hikashop.com/index.php?option=com_h...ow&Itemid=91&lang=en
The way that you restrict the selection of the options using a special variant is not the best one.
Because HikaShop will try to add the product and the options too ; and it will add the product but it will block on the addition of this specific option (and it will result the error message).
I think we have something to improve during the check in order to display a more appropriate message but the finality is the same.
If you really want to not pre-select a value for the options, the best will be to modify the dropdown directly and add some checks in order to refuse to continue (when pressing the "add to cart" button) using some javascript.
It's the best way I see.
I'll update the HikaShop TODO list in order to note that could be improved in HikaShop ; maybe adding an option can be a good thing in HikaShop (but I won't be able to give you any schedule for this implementation, we have a lot of tasks in our TODO list).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.