2.6.0 > 2.6.2 upgrade. Lost access to Admin login

Have you checked wp-config.php ?

Are all the top 3 settings correct?

// ** MySQL settings ** //

define('DB_NAME', 'Your_Database_name');
// The name of the database

define('DB_USER', 'Your_Database_Admin_Username');
// Your MySQL username

define('DB_PASSWORD', 'Your_Database_Admin_Password');
// ...and password

define('DB_HOST', 'localhost');
// 99% chance you won't need to change this value

define('DB_CHARSET', 'utf8');
define('DB_COLLATE', '');

Yes, the redirect seems to be broken, or atleast crippled.

If I access the admin via myblog.com/wp-admin it shows me the login screen regardless if I’m previously logged in or not, and always returns me to the login screen regardless of successful login or not.

However myblog.com/wp-admin/ (with trailing slash) redirects correctly with or without authentication in between.

IIRC this behaviour (requiring the trailing slash) wasn’t there in previous versions. To non-techy users this is also a possible cause of confusion and desperation. (Witnessed with my gf.)