Carolyn,
I used the following link: http://<servername>:port#/BP/_layouts/ChangeSiteMasterPage.aspx (The underscore was missing before layouts.)
1. Site Master Page is set to 'BusinessPortalDefault.master'
2. System Master Page is set to 'BusinessPortalDefault.master'
3. Alternate CSS URL is set to 'Use Microsoft SharePoint Foundation default styles'
I don't see a 'default.master' option for Site Master Page. There is a v4.master. Should I try that?
~Casey