Animation in Humanoid Vs Legacy

I am using mecanim animation system of unity 5 free version I am facing some problem while using rig type Humanoid for my character animation. Here is the problem- "I have character model with some animation, whenever I run that character with Rig type Humanoid the toe of my character is submerging in the ground. and the same animation in preview window with Rig type legacy or generic is working fine"

I need suggestion to overcome this problem. by enabling foot IK the toe submerging problem solved but the animation goes weird than original one.