The invalid CD Key error is usually due to trying to install the wrong patch for your version of ArmA.
Most versions should install the international 1.05 patch first, then the 1.08 patch, then the 1.14 patch. If you're unsure of which version you have, try this method.
505 versions (should have the 505 logo on the box art) should install the European 1.05 patch, then the 1.08 patch, then the 1.14 patch.
Atari versions (should have the subtext "Combat Operations" rather than "Armed Assault") only need install the 1.08 patch, then the 1.14 patch.
Hope this has been helpful
Internation 1.05 patchEuropean 1.05 patch1.08 patch1.14 patch