Most air attacks in my current save give this error. Saving+restarting doesn't fix it, and the error appears in every battle. Here's the save, in the middle of a battle - just let it run, let enemy aircraft attack your(my) fleet and you should see the errors pop up quite often. Some air attacks still "work".
From what I can see this error makes the air attack glitch out. For example, the only message that shows up is "35 enemy Chedworth B dive bomb BB Deutschland" . No AA fire, no damage results, nothing but that message.
Or this one, which is in your running battle, on the ground at Rosyth with -307 (!) experience, one of the oldest squadrons in your game (curiously I do not find experience saved in the .sac file, I presume that is loaded/saved from/in the.bcs file also for battle):
AU3AircraftTypeId=-1 AU3AircraftType=Kingham AU3Id=474 AU3AircraftNumber=3 AU3DesiredAircraftNumber=4 AU3Role=4 AU3Nation=1 AU3Experience=-307 AU3Name=474 Squadron AU3HomeBase=Naval air station Rosyth
I have played another save from 1920 to currently 1947 and this error has started appearing again. So that's two saves in a row ruined by TAirUnit.AttackShips Procedure. Are the developers aware of this issue? Have the saves been looked at?