All posts “uncategorized” after upgrade

Just upgraded to 2.6 tonight, and now virtually all of our 46,000 posts – yes, 46,000 – are showing up “Uncategorized.” Please note, “Uncategorized” is not a category we currently have – so when I browse the posts, the word “Uncategorized” does not appear as a link. They are floating in limbo.

I’ve installed the Batch Categories plugin, but it does no good as it can’t see posts that aren’t already in at least one category. To be clear: 46,000 posts suddenly have no category at all.

Please tell me there is something I can do other than opening them one by one and assigning them to a category … please …