Why I can't substitute or change formation sometimes

Solution 1:

Answering my own question. I am not sure if this is the correct answer but I have observed it is something to do with switching of controllers after the game has begun. I can't tell exact scenario when this issue will arise because this happens only when you are playing online and it involves multiple scenarios (explained below) and more over you don't have privilege of pausing more than two times in each half and I don't want to give away goals to opponent trying this :)

Switching Controller during game play:

You will some time need to switch the controller because of low battery and you picked second controller or may be you want to change because you picked a bad/broken controller. Here you have good chances that you are not allowed to substitute players when the second controller you picked was already turned on by your friend who has a profile in xbox. May be I should turn off both the controllers and turn on again.

Kinect & Auto detection settings:

I have observed this happens mostly when your kinect is on and it has auto detection settings is turned on. I guess there is some feature implemented by EAS for cheat prevention.