Dooyar,
This is what I did (I had a paid for version 1.1.1.1 A10-C) running Win7 64.
1. Uninstall A10-C, but don't do anything with your registry.
2. Delete any saved games etc
3. Download DCS World and install.
4. Download A10-C 1.2.0 module (approx 700mb) from DCS website.
5. Run installer.
Your registry should pick up that you had a previous version of A10-C and work. I had no need to buy new copy or put in previous activation key.
Hope this helps, :thumbup:
Cheers!
Snpusher