Today I upgraded to Ubuntu 17.04. I get to the login page and type my password correctly, then the sign in message disappears, it stays for a few seconds, then returns and asks me to type the password again.
I am sure I am entering the password correctly since when I tried entering a wrong password, the computer displayed "Wrong password. Try again."
Like Dolan said check the caps lock. What you have is likely a very common error, probably the most common on askubuntu. This command has gotten me past that same error on a fresh install with 3 different computers and is harmless if it does not work (open the tty1 bash before login with ctrl+alt+F1 and enter your login and password, then input this command):
sudo dpkg --configure -a
This will configure any pending packages which you might need in this case to get past the login screen. I've had to enter that same code at the tty1 on all of my fresh Ubuntu installs before I could login. Then go ahead and do
sudo service lightdm restart
to get you to the login screen again.
