Hi regis9,
I contacted FSS as I was experiencing the same issue.
They suggested the following steps, which worked for me after trying several other fixes:
Working fix:
Close the sim completely.
Uninstall all E-Jets variants (including the Freighter variant, E17X and E19X).
Restart the sim.
Reinstall only the variants you want (E17X and/or E19X).
After doing this, the activation box disappeared and everything worked normally.
Hope this helps!