Ok, i got it.
Here is what happened. I installed a new SSD and installed DCS World on it. I also reinstalled my Win7 after Win8 wasn't running as expected on my raid system. So I installed DCS World, A10C and FC3. But, i never activated A10C cause i never started it. But the system asked for the serial of the A10. FC3 was activated manually as written in my post above. Strange, but finally it works :-)