Well, "don't work" is a bit vague. I'll just have to assume you mean that there are no errors, but no message is shown to the players.
Well, the only thing I can think of is that the AI soldiers aren't on the same side as the players (in which case it isn't obvious why they would be radioing the players with a message when they are getting killed off). In this case, you'd just want to use globalChat, not sideChat, so the player would see it.
The other possibility is that you are wanting a solution for an MP mission on a dedicated server, but this question isn't in the MP forum, so it can't be that.