It means one of 2 possible things.
the user firstname.lastname@example.org does not exist or you are entering the wrong password. How did you migrate your data from your local machine to the server? You can look in the mp_Users table and see if the user exists and what the password is.
logging in just sets a cookie, if somehow the cookie is being blocked then it would behave as you describe. Possibly you have some browser plugin or privacy guard preventing cookies, possibly the firewall could prevent cookies. I suggest try accessing the site from a different machine or using a different web browser and see if you get the same result.
Hope it helps,