If you get this error after joining a mission or anywhere, then I have the solution for you.
1. Go into you ArmA 3 folder under steam/steamapps/common/arma 3/
2. Go into folder @AllinArmaTerrainPack and to addons
3. Delete both files named "AiA_BaseConfig_F" and "AiA_BaseConfig_F.pbo.AiA_TP_2015_01_01.bisign"
4. Download this and put it into the same addons folder:
https://drive.google.com/file/d/0B32HlOEh0uv6eXZVX0xyTnl6UHc/view?usp=sharingDO NOT try to overwrite, since Windows overwrite function can make files corrupted.
If you do it exactly how the list says, it will solve the problem.