What's the password for the Internet Explorer interface?
This is usually the same password that you use to access your DVR directly. Some defaults are 111111, 888888, or blank.
Make sure to use Admin as the username and not admin, it is case sensitive!
If you are positive that you are using the correct password and command port, and it is still not logging in, I would check the setting for "IP Access" and make sure it is disabled. See more information here: http://kb.zmodo.com/index.php?solution_id=1327