Well,

Looks like I am asking something which I am not sure of.

Can Mac Address of two systems be same? As far as I knew till now, it cant be. But my bro who was facing wireless authentication failures while connecting to WiFi found that two users with same MAC address was the reason of authentication failure (The Admin checked the logs and told this).

I am still not sure if its possible. Correct me if I wrong and share your opinion.