[FG28_Kodiak]

Your error:
if (SaidToGroup == true) return;
you leaving the method, but i think you will only leave the foreach, so you must use:
if (SaidToGroup == true) break;

and g.candidates() returns AiAirGroup[] so you should use GetItems() to get the Actors.

Corrected code:

private void sayMessageTo(int army, string msg)
    {   // send a speech message to all players in specified army (1=red; 2=blue)
        foreach (AiAirGroup g in GamePlay.gpAirGroups(army))
        {
            bool SaidToGroup = false;
            foreach (AiActor a in g.GetItems())
            {
                if (SaidToGroup == true) break; // speech already said to group
                SaidToGroup = true;
                (a as AiAircraft).SayToGroup((a as AiAircraft).AirGroup(), "Ready_for_takeoff");  // for testing only
                //a.SayToGroup(a.AirGroup(), msg);
            }
        }
    }