in my FSX Steam, there is no Add On Manager for FSDT.
This is the one and only problem. Unless you fix this, it would be completely useless to try other activation method, in your case the Offline activation.
It's not very clear what do you mean with "transfer your products" ? You mean you tried to "move" them from one sim to another ? This will never work, and will just cause a big mess. Also, there's only ONE safe way to upgrade from FSX to FSX Steam and is:
- Uninstall all your add-ons from FSX first, at least those (like FSDT) that have a proper Uninstaller.
- Uninstall the original FSX after you removed all your add-ons.
- Install the FSX-Steam version only after you are sure you removed the original FSX.
- DO NOT install any add-ons yet, but RUN FSX-Steam at least once. If you don't do that, many add-on installer will fail, because FSX Steam will create all the registry keys during its first run, this is different than the FSX DVD install.
- After you ran FSX-Steam once, you can start installing all your addons, using the own installers.
- In case of FSDT addons, be sure you use the most current version of their installer.