I just had a scary few minutes. I upgraded this site to WordPress 2.6 last night and today couldn’t log in; or rather, I could log in but the admin area kept throwing me out.
It turned out to be a problem doing the upgrade to 2.6. I should have disabled all my plugins first but didn’t. This post helped me, as well as the Dreamhost control panel. So for future reference, if this happens to you, rename your “wp-content/plugins” folder to “wp-content/plugins-old” then log in. The upgrade will happen, then you can rename the folder back to “plugins” and it should work.
And to celebrate, here’s what we’re all having for breakfast: