I switched to Arma3 RC branch and since then as soon i load any mission or create a new one i get a new messagebox with the warning.
"Cannot load texture a3\armor_f_beta\apc_wheeled_02\data\ui\map_apc_wheeled_02_base_ca.paa."
The missions however load just fine without any problem.
The warning is somehow triggered when the "The CSAT modification project" mod" (https://steamcommunity.com/sharedfiles/filedetails/?id=441854566) is loaded, but only with Arma3 from RC branch. Switched back to main branch and the warning did not came up, switched back to RC branch release and got the message again with just that mod loaded.
Not sure if its a Arma3 problem or a mod problem, but as it does not happen with mainline Arma3 there seems to be some form of regression in Arma3.