How to down grade a group 700 sitting at version 6.0.1 to version 4.1

Want feedback on this.

I tried to factory default by USB where I copied ver 4.1 and the activation code the same in Sw_keys.txt

But every time the unit defaults to ver 6.0.1 only i.e it does not down grade to ver 4.1.

We need to down grade the unit to make it compatible with Cisco VCS ver 7.2.2 (older version only compatible with lower versions of Group series)