Archives stopped working

My archives were working fine, and then . . . not sure at which point they stopped.

I did install multisite a couple of days ago, but I believe they were still working after that. Now, whenever I go to the monthly archives page for each blog, I get a “Not Found – Apologies, but no results were found for the requested archive. Perhaps searching will help find a related post.” where there should be posts.

Site URL: http://davidfranklin.net/blog/

thanks!