Did you check your firewall settings?
Check this out to see if helps:
Online Kingdoms Registration issues
1) Copy Paste your CD key, using Cntrl + V command. Note you might need to hit the keys twice for it to work
2) Disable Anti Virus and Firewall - and if that works set DoF.exe and or Mithrill.dll as exception
3) If you get error - the key must be 25 or 29 characters long - check the key, try entering it again and again, sometimes it might take couple of tries
4) If you get error - CD key already in Use - please contact email@example.com and let them know there is an issue with your CD key.
Community Manager - feel free to PM me about any game related issue, bug, question...