Why do my characters keep sinking into the ground?

I am using the Basic Shopping Mall model as my environment, purchased from the Asset Store, and it has a ground, because when I put my Nerd animated 3D character on it, the Nerd walks across the shopping mall fine without issues.

However, I also downloaded an animated 3D woman character from the Asset Store, which came with textures and all, but when I import her the skin texture isn't showing and she appears in the generic grey colour. When I start the game, she sinks half way into the floor. She has an associated Character Controller component and a Capsule Collider, too.

Same with this woman I created using the Daz3D studio Genesis 3 model. She has skin, hair, clothes and skin texture, but upon import she loses that and just appears as a generic grey woman in Unity3D. She also has a Character Controller and Capsule Collider, but she doesn't sink into the floor.

Why is this happening?

 

Most probably this. Check out the answer by Emericanized