Invalid CD key error may be present if you're trying to apply the wrong patch. (I seem to remeber the 2 previous posters went on a witch-hunt for this exact reason the last time this issue arose...)
I'd suggest starting from a clean install if you're having trouble. Because there are a lot of problems that'll arise if you've installed the wrong patches. Also, there's a chance that playing a copy against the same copy on a LAN will activate FADE. This may be causing trouble with patching.
Firstly, you need to identify which version you have. There are 3 main versions, 505, Atari or Morphicon. It should say on the box or on the splash screen the name of the publisher.
If you brought your game in Germany, Russia, Czech or Poland you'll probably have the Morphicon version. You need to install this version of the 1.05 patch:
http://www.armedassault.info/index.php?cat...&setlang=enIf you brought your game anywhere else in Europe (and I think Australia too) you'll probably have the 505 version. You need to install this version of the 1.05 patch:
http://www.armedassault.info/index.php?cat...&setlang=enIf you brought the game in the US, you should have the Atari edition (this is easily identified, as the box says "ArmA - Combat Operations" rather that "ArmA - Armed Assault"), you don't need to worry about the 1.05 patch, as it's already installed.
Once you've got 1.05 up and running, you need to install 1.08, found here:
http://www.armedassault.info/index.php?cat=patches&id=1Then install 1.14, found here
http://www.armedassault.info/index.php?cat=patches&id=9Congratulations! This is the latest stable version of ArmA.
If you want to run the absolute latest version you can install the 1.15 beta, this isn't a finished patch and will install to a subdirectory. I'd advise using the 1.14 version though.