Game launch problem - some files not found

[goMatz 0]

I'm playing Arma 3 for years, never had a problem. Last launched and played the game faultlessly last Sunday. Started game today, Steam starts OK. When I start the game on the Arma3 screen, it starts initializing add-ons but I get a popup that Addon "A3_BaseConfig_F" requires addon "A3_Modules_F_Heli_Misc". If I click OK it continues loading briefly but then I get another popup saying Include file A3/ui_f_curator/UI/defineResincl/Design.inc not found. and the whole thing aborts. If I try launching the game with optional DLC (SOG Prairie fire), I get the above and an additional popup that bin/config.bin/Cfg/Vehicles/House_Small_F/DestructionEffects/Smoke1/: Cannot find  base class "Smoke1". And again Arma3 aborts. 

I checked game file integrity via Steam and everything seems OK there. I did not have any updates (Windows or others) or other games or programmes installed or deleted since I last played a week ago.

Any idea...?