After installing version 1.1.0a the username / password aren't working

I've installed Kali before and didn't have any problem.

With the latest version 1.1.0a as a first install on a laptop, the installation program (graphical version) asked for a password (no username).

After the installation, Kali loads oke, but shows a login form with a single option: Other.
When clickin on Other, i'm asked to enter a username (root ??)
and a password (the earlier given password i persume ??)

this combination isn't working: Authentication failure.

- what is the correct username after installation ?

By default, yes, 'root' would be the typical user you'd log in as. If you established a plain 'user' account, then you could log in with that, as an alternative.
The password for the 'root' account would be what you've entered during system install/build. If that isn't working, then you likely have a disconnect between what you think you entered then, and what the password actually is.

The most straightforward method to resolve would be to simply reinstall Kali and be more careful with assigning a password for 'root'.

I installed Kali for the first time yesterday and also get login screen ¨Other¨ I logged in with ¨root¨ and my configured password during the installation of Kali.

My configured account during installation was above ¨Other¨ but do you don´t use this account? Is it not that you are loggin in with your normal account, or are you always root by Kali? Can someone provide me with some clearness?

my instalation disk of kali didnt even ask me for user/password. only set root password.

Good security practices dictate usage of a plain 'user' account, vice always being logged in as root. One should switch users to do commands (via sudo) when such privileges are required.

If you've only created a password for root, and haven't established a user account, then the root password will be whatever you chose at installation time.