Board Game Arena

I want to play the brown tile on the top of the another brown tile (bottom-right in the figure), however the system disallowed me to do so. I searched through the rulebook but not found the relevant details. Excuse me?

It seems that I cannot upload the image.. At the close-end time there were three empty places, I take three tiles including a brown one, but I cannot place the brown one on top of the another brown one. It is part of the rule?

Are you sure you are posting this in the right forum? This one is about Forest Shuffle.