I've come upon a bit of an issue today, when I was trying to log into a subpage in a multisite - when logging in, it would just revert back to the login page with 0 feedback.
- reuploading all core files
- reverting to default htaccess
- disabling all plugins
- disabling all themes (using twentyten)
When i put in a wrong password, it still says wrong password. But on a successful login, it just redirects back to login.
I can login to the main page just fine.