It appears to me that you are not passing the username and pass along to the subsequent links.

Once you log in and click the link, you are not passing along the $username and $pass to the next call which brings you back to the login screen, which I believe because you have no $username and $pass, gives you the error.

(I'm pretty sure that when you do the deck transition, it still calling the script again which means the username ans pass are long gone)

I haven't done too much with WML but you should check out the following CPAN module, CGI::WML, this subclasses CGI.pm to generate WML output.

Hope this helps.