Oh dear, I have an identical problem, but it cannot be resolved using the above solutions. I’ve just upgraded from 2.5 to 2.6 and I get stuck at the login screen (“ERROR: Incorrect password.”). I’ve:
1) Cleared the cache, cookies, history.
2) Tried another browser (I use Firefox, but tried logging in via IE and Safari).
3) Reinstalled the whole WP installation.
4) Manually reset passwords in database + added a new user (with admin access).
5) Repeated steps #1-#4 over and over…
Still no cigar. Any other ideas would be great! Thanks in advance…