Trouble logging in with MySQL

Hi very new to Pentaho and very interested in the dashboards.
IN my setup I have Pentaho 5.4, CentOS and MySQL.
I have just configured a fresh install of Pentaho 5.4 for MySQL and started for the first time.
I watched catalina.out and there were no errors.
But....when I go to login with Admin/password I get a pop up window which says Login Error
There are no recorded errors in Catalina.out

So, I dont understand
1: why I cant login
2: where the user credentials are stored - i.e. I cant check if they have been created
3: how the default credentials are created.

Any help appreciated

Nick