Why can’t I get Outlook to connect to my ISP?

I have a friend who recently bought a MacBook Pro to replace her pc. She had Apple migrate all her data over to the MacBook Pro. We then installed Office for Mac 2011. Her preference was/is to use Outlook for her email. This only became known to me after I got her email set up and working in Mail (Apple's mail app). I then proceeded to set up Outlook with the exact same settings that I successfully used for Mail, i.e., incoming and outgoing servers, ports, SSL, authentication (name and password), etc. There was a brief time when it was up and running, but inexplicably, this is no longer the case! The error message I get continues to point to authentication and her ISP's denial of services. Unfortunately the tech person for her ISP could not help me. Has anyone else had this problem? Any help would be appreciated.