|Next time read the manual before you go through the setup wizard.|
It says quite plainly in the manual:
A password request screen will appear. (Non-Windows XP users will see a similar screen.) Leave the User name field blank. The first time you open the Web-based utility, use the default password admin. You can set a new password from the Administration tab’s Management screen.) click OK to continue.
So what you should be doing is entering admin for the password. If it doesn't work with a blank username and 'admin' for the password, use 'admin' (without quotes) for both username and password.