"Control of XXX's untis has been taken away."?!

This message appears occasionally in my map, always after cinematic. However, there doesn't seem to have anything to do with the game play. Can someone explain why this happens? How can I solve it? Although it doesn't affect game play, it's really annoying.

Thanks!

I found the reason of this bug in another forum. It was because I try to let e.g. set player 1 allied with player 1. So it is solved easily. =)