Local Server Installation - Login Error

Hi All, 

Finished the installation of the databases and webserver on the machine, following the installation guide it reached a point where it told me to test the application and login for the first time using preset credentials.

I tried inserting the standard credentials but I would get the error message "Unable to log on user 'Administrator'.  The password was reset and needs to be changed." and it does not allow me to change the password (see screenshot below).

This is a fresh installation and the standard credentials were never used before, did some error occur during the installation or is there something I have to do to make it work correctly?

Any help would be greatly appreciated,
Alberto