So, let's create the username home folder then. To do that just follow this steps:
1 - On the login menu press Ctrl + Alt + F1 to open the terminal
2 - Log in with your user
3 - Execute the commands
sudo mkdir /home/username
sudo chown username /home/username
4 - Then press Ctrl + Alt + F8 to return to the GUI
Hopefully now you can login :)
Thanks to @MariusMatutiae for this aditional step
When a new user is added, his home directory is endowed with a small
number of files and directories, some of them hidden. They can be
found in /etc/skel, and be copied over to the new home directory.
After you login for the first time, open a terminal window and type the following command:
cp -a /etc/skel/. /home/username
This will copy all the files inside skel to the username folder.