Rather strange, as it does work for me... I'll try to explain the steps:
1. Create a new Action, and find the Action named 'Follow Unit Group with Camera', it's in the 'Camera' tab.
2. Set the player to the desired player.
3. Set Unit Group to 'Convert Unit To Unit Group' (Source: Function).
4. Set the Unit to your desired unit to be followed.
5. Keep Clear Current Target.
It should work, and if not, then I don't know. Anyways, shutting down my computer for now, so I'll see tomorrow.