If you can not login, try to remove your cookies from your browser.
The following is a manual for Internet Explorer:

Go to the settings page of your webbrowser:



Then delete the cookies from your webbrowser:



You now need to confirm the deletion of the cookies:



After that close your internet browser and open it again.

Then it should work....

Otherwise send an email to flirtbox gmx.com

The same can be done in firefox. Tools > Options > Privacy > View cookies

Find flirtbox.net and delete that cookie.

Toby suggests logging out after every session, but I know most of us are too lazy to do that