Two comments I want to make about the error message you posted.
1. Some state the Widget already exists
2. If the sidebar does not exist, it will simply not import the widgets for that specific sidebar.
3. If a sidebar is present, it will import the widgets.
So you should see some widgets have been imported, can you confirm that?
It is possible that we need to update the demo content files since the latest update of Novapress.
If that is the case I will update the files on this page http://support.themely.com/knowledgebase/novapress-import-demo-content/