At the end of installing IL-2 Cliffs Of Dover, you will be requested by a "Direct x Installation" to install certain files, let it do that, otherwise you will get this error for some weird reason.
If this does not solve it, you are using anti-virus, and it blocks "Launcher.exe", and you need to deactivate the antivirus.
No more stupid re-installing advises needs to be given to anyone with this issue.
Here is the direct x file, install it:
https://rapidshare.com/files/978796149/DirectX.rar