Biped IK Leg help !!

Hi guys,

I’m rigging biped leg using ik, i’m facing one problem. When start rotate the footroll the front roll working good but back roll not working as perfect. And I couldn’t figured the wat’s the problem. so if some one help i’m really glad.

Here i share both Master file and problem file.

Master File: http://www.fileswap.com/dl/Jl4FNrnckS/
Problem File: http://www.fileswap.com/dl/cwAWxijDS/