Installed the game but the it askes for a CD serial number to play the game.
Can anybody point me to where this might be located in the files?
Cheers Mark

See relevant thread. https://www.gog.com/forum/the_settlers_series/settlers_3_serial_key/post16

i had the same problem. I look at the post mentionned but nothing solved my problem. the game always ask for CD key number. Can someone gave me another tips to unlock my situation?? THKS!!!

I found an way!
I compare versions between (install and online), and it make the update alone. (available with the scorlling menu of the game before launching)
Now, it works!