I upgraded to 2.6
All seemed to go well until it asked me to log in again.
It would not let me in.
I was using the correct password as Firefox was entering it for me.
Reset the password.
Cleared the cookies still nothing.
If I go to my site and login there, it works fine, I see my username.
If I click on "Site Admin" I can't get past the login screen despite being logged in !
If I click on my name to go to my profile page, or if I click on "Write A Post" I can get into the admin are no problem at all !