are sure you have the correct username and password
are sure you are using the https:// version of the page when trying to log in
could you please email me at email@example.com just say whether you get the white page that says “The password you entered for the username bla bla is incorrect?”, that the user name is unknown or whatever. Include the user name in the mail, but of course not the password. Thanks in advance. :) It seems some people can log in, some others not.