It was working in ours until the past moh update. It used the chat trigger to yell on screen just recently stopped working. @yell
The admin.yell command is gone in MoH Server around R3.
Before that server version it was in but did nothing accept replying with an OK.
Actually you are talking about a plugin, guess you mean the InGameAdmin.
While talking about problems with it it would be a good idea to list all versions of
the tools you use and the versions of the plugins.
The InGameAdmin provides an @yell in game command, but (!) on MoH servers this command
is translated into an admin.say command send to the server where on BFBC2 it sends an admin.yell
Feel free to check / report your plugin / procon related questions at the procon forum.