Opening Outlook – Could not change to that identity – error

I have just purchased a new MacBook Air and just installed Microsoft Office 2011 Business.  I want to set up Outlook to use my 'gmail' email account and am trying to set this up.  When I try to open Outlook, for the first time, it asked me to select an identity.  I select Main Identity, not sure what this means, I am getting a message "Could not change to that identity. An unknown error has occurred in Outlook".  Also when I selected Quit it happened.  I have gone into 'preferences' 'mail, contacts & calendars and put in my gmail account, but still get error.  Eeek... What am I doing wrong?