Make sure your browser is set to accept cookies.
If you don't want to accept cookies in general, you will need to add www.tiwaz.org to
the list of domains to allow cookies for.
For Internet Explorer 6 go to Tools - Internet Options - Privacy. On the bottom of the tab, click the Edit button, enter "http://www.tiwaz.org" in the text line and click the Allow button. Click OK until all dialog boxes are closed again.
For Opera look under File - Preferences - Privacy. Make sure the Enable Cookies box is checked and adjust the detailed settings as preferred.