Failure to do login in the initial screen

[Guest]

I reinstalled kubuntu, my root password is correct, however, how much does it open the login screen, and I type the password returns the error message: authentication failed. For this reason, I can not log in to the system. Can you help me?

Note: The administrator password is correct ok

[Snowhog]

Passwords are case sensitive, but also, Ubuntu has a mininum size for a password, which I believe, unfortunately, is ignored when you specify your password during installation. What is the length of your login password?

[Guest]

My password has 11 character like that "fibrass@0283"