I upgraded my installation of wordpress over the weekend and the “can’t login to admin panel” problem kept me pulling my hair for two days. I am listing down the steps I did for the sake of the record.
1. I cleared my cookies and authenticated sessions, even tried login from a different browser, no success.
2. Reset my password, still no success…
3. Upgraded my wp-config.php to include 3 secret keys (taking help from wp-config-sample.php), no success…
4. Stumbled upon this thread, but it didn’t help me since I wasn’t using Admin SSL.
5. Then I came across this article, so I renamed my plugins folder, logged in, renamed it back to plugins, and everything works now.
and God, Akismet is a blessing. I didn’t have Akismet for 2 days and my inbox was full of all sorts of spam comments from wordpress.