I set up my own scenario with the editor, and found that if i added 6 enemy groups and 6 of my own and 2 helicopter groups and 2 enemy vehicle groups the fire button would not work all the time. It was almost like I had to wait for the others to finish shooting before I could?
(the game graphics were set to full and i had overcast 100%, lightning 100%, wind and waves 100%) {F19284}