Things that come to mind:
1. Make sure that you have cookies enabled. If you don't, CyberNations will be able to create a game session but you won't be able to access it, and you'll be forced to repetatively log-in without apparent success.
2. Check if your browser is switching between http://www.cybernations.net/* and http://cybernations.net/* during your session. If it is, then that's the problem - I've had that a number of times (usually either problems with links stored in messages or browser problems rather than a problem in the game); at each switch, CyberNations can't access your session cookie forcing it to create a new one, effectively locking you out of your old session and forcing you to repetatively log-in.
3. Make sure that your browser's cache for each page expires correctly. It should normally, but sometimes won't. If it doesn't, then that will likely cause problems.
Failing those three things, I wouldn't know what it is. Could be a bug. Hope this helps though.
