individual posts and archives not viewable

I just re-installed WP after a hack; I imported the sql file that I had exported prior to wiping out my previous installation.

Now that the blog is back up and looking good (Twenty Ten 1.4-wpcom), I find that clicking the link for an individual post or an archive month brings a 404 error page.

Kate blog

The url path (after the site url) is something like: /archives/848
or: /archives/category/rio-grande-river-gorge (category widget)
or: /archives/date/2011/09 (archive widget)

What is the solution?
Thanks,
Eric