After 5 days of waiting for any response, I decided to write to the german support too yesterday. Now one day later I finally got an reply from the german support, that there are problems with the anno 1404 keys and they are currently trying to figure out why.
The english support is a joke...
Wow..that sucks..at least the german guys responded
Got response and the solution today:
In Anno 1404 Venice at Profiles Click "Create new Online Profile", and log in with your Uplay Name
, NOT your UPlay email adress, otherwise it won't work.
After you're successfully logged in, you should be able to click Multiplayer Internet in the main menue. If you click it, a window will appear, where you have to write your key into.
Thanks to the support, better late than never.