Not all categories are eligible to list with multi-variation. There is a list on ebay that indicates which categories are eligible, but I find that the list is not up to date. You can only be sure if it's eligible by actually trying to list it and then see if the multi-variation option shows up.
If you are saying the multi-variation option shows up, but it's not working? Then I suggest you close that listing attempt and start a brand new listing from scratch, not a "sell similar", and see if that works for you.
