If you're using the Macintosh version, copy the Blockland folder to your applications folder and run the game from there. The game does not run properly from the mounted image because it is a read-only image.
If you're running the windows version, make sure that windows firewall and any other security software you have installed is set to allow Blockland to connect to the internet and access the hard disk. Other than that, you can make sure you're entering the key correctly by copy and pasting directly from the email.