athineos: ... turn off any antivirus program you may have. ...
Never turn off your virus protection!
I don't know why people are recommending to do this. I've been playing computer games under AV protection for more than 20 years, and never encountered one game which crashed while AV was on, but worked when AV was off (I tried it a couple of times in the early years).
There were games my AV program complained about - then there was a message stating why, and I could make up my mind to either accept the complaint and to not play the game, or to tell the AV program to let the game run. You may also contact the developers of such a game and request that they do something about the issue.
But turning off virus protection globally for your whole PC has the potential to open a Pandora's box of virus and Trojan attacks, and very likely doesn't help your game running. Also, if AV sees an issue with a game, then it puts the files it has an issue with in quarantine, and you have no chance to use them without restoring them first.
Once again: Tell AV to let your game run, if AV tells you that it has an issue with the game and you think it is acceptable for you to ignore the warning, but never turn off AV completely!
Sorkvild_Raven: I tried and either get crashes or freezes. Whenever I choose campaign, random game or a scenario there is a crash sooner or later. Game also tells me I'm low in hhd space :/ 180 GB of free space.
EC-HQ: confirmed. I get the same warning at every start of the game.
I get this message, too. It means that the game checks your PC for sufficient disk space, and doesn't interpret the values correctly. Just ignore it.
Is there a way to prevent the message from appearing whenever the game starts?