Demo crashes

When I develop a new application using "rails demo" then run "ruby
script/server" WEBrick loads fine. I point my browser to
http://localhost:3000. The Welcome aboard page loads fine. But when I
click on "About your application's environment" I get this error:

CGI::Session::CookieStore::TamperedWithCookie in
Rails/infoController#properties

CGI::Session::CookieStore::TamperedWithCookie

When I try "rails -d mysql demo" I get the same error.

any ideas?

mike